How to lock a PDF

How to lock a PDF from editing, copying, sharing and printing

How to lock PDF documents with and without passwords and why DRM is the best protection software for creating secure PDF files so they cannot be edited, copied, printed or shared.

  What is a PDF Lock?

A PDF lock is a method or technique for denying access to PDF-encoded information, such as locking a PDF with a password or registration code.

Some types of PDF protection are achieved with hardware – typically a ‘dongle’, which is a piece of hardware that must be present for the PDF to open. Most types of protection are implemented in software, and these may require entry of a password, registration codes, user identification codes, as well as network or machine addresses to be present or provided.

  Methods to lock PDF files & documents

PDF protection has to make use of encryption to prevent anyone from being able to process the PDF without a suitable key.  However, there are different grades of protection:

1. The simplest form of protection lets you encrypt your PDF with a password, which allows access to the content it is protecting.  This is among the least secure methods – users can easily remove passwords.
2. A more secure solution will go much further.  It checks independently that the user/machine it is working on has been registered for the document in question, that it can obtain secrets needed to form the key, and that the use of the key is valid.  This kind of PDF protection is more subtle, and breaking it is much more complicated.

While a PDF lock shows some of the characteristics of physical locks – only opening at certain times and so on, it can go further by addressing how the file you’re protecting is subsequently used.  So, a strong protection system should consist of a granular and layered architecture – decide what features are to be unlocked, and even for how long, or under what circumstances – rather than a simple on/off mechanism.  Most importantly, it must be able to prevent authorized users from passing on information after it has been unlocked.

That said, we’ll be covering the full range of methods to lock PDF files and make them read-only to educate readers on their pros and cons.  This includes password and certificate security, as well as how to use PDF DRM software to securely lock PDF files from opening and restrict how they can be used.

You will learn:

   Why lock PDF files?

Regardless of whether you’re a large enterprise or a small business, the time will come when you need to know how to lock a PDF from editing or viewing.  Perhaps you have some meeting notes you need to share with an outside partner, a contract draft, confidential or sensitive documents, or a yet-to-be-published ebook.  In all cases, it’s vital only authorised parties can open and interact securely with the content.  When locking a PDF document, organizations are usually looking to fulfil one or all of these requirements:

• prevent content from being edited
• stop content from being copied and pasted
• stop form content being changed or stop data in form fields from being edited after submission
• block printing, allow only degraded printing, or restrict it to a specific number of prints
• prevent it from being downloaded or saved
• restrict use to a machine so it cannot be distributed to others
• restrict access by IP address so it can only be used in certain locations
• prevent changing of display settings so that content is presented in the way the document publisher wants

  How to lock a PDF with a password & why you shouldn’t

There are dozens of freely available tools that will let you lock a PDF with a password, but the most common is Adobe Acrobat.

However, Adobe Acrobat and other password-based systems are inherently flawed:

1. Any user that receives the password can share it with someone else.
2. PDF password removal tools can remove Adobe PDF password restrictions in seconds.
3. 16-character ASCII passwords can be brute-forced in an hour.
4. Passwords are time-consuming to manage.
5. You need to have a secure way to distribute them.
6. Secure passwords are hard to remember, so users tend to save them to plain text files.
7. You have no way of tracking who has access to the password.
8. As soon as you share the password to open the PDF, it becomes trivial to remove.

Essentially, PDF passwords only offer the appearance of protection.  Ideally, they shouldn’t be used in a business environment at all.  They should only be used to lock non-sensitive information that won’t be leaving your local PC.

If you want to lock a PDF with a password because you are just storing it locally, then we cover below how to lock a PDF from editing using Adobe Acrobat and SmallPDF (online PDF locking software).

How to lock a PDF document with a password using Adobe Acrobat

Follow these steps to lock a PDF document with a password from opening or editing using Adobe Acrobat DC Pro.

1. Open your Document in Adobe Acrobat and select the “Protect” option in the sidebar.
   

2. Click “Protect Using Password” in the top bar.
   
3. Tick “Viewing” or “Editing” and enter a secure password.  If you must use a password, you should follow the guidelines for choosing a strong password to protect PDF files to create one that can’t be brute-forced easily.  Bear in mind, however, that Adobe restrictions can be removed (or just ignored) without the need for brute-forcing.

   If you want to lock a PDF from editing, select the ‘Editing’ option.  You can also select whether you want to allow printing, copy-paste, etc.

   WORD OF WARNING:  Bear in mind that locking a PDF with a password is a complete waste of time – they can be trivially removed using free PDF password removal tools.

   

   Locking a PDF from opening with Adobe Acrobat

   Press “Apply” when you’re happy with your password.

   Locking a PDF after signing

You can use the same process to lock PDFs after adding a visible signature to them.  This makes it clear to users that they’re viewing the final, approved version of a document that should not be modified.  Due to the flaws mentioned earlier, though, it doesn’t actually prevent them from editing the signed document or even removing or changing the signature image.

Adobe digital signatures

Adobe has at least attempted to address this with a second approach to PDF locking.  Certificates are used to lock a document after digitally signing it.  Signatures are linked to users’ private and public keys, which allows the software to inform recipients that the sender is legitimate and that the document has not been modified after it was signed.

While digitally signing PDF files and encrypting with certificates is more secure than passwords, Adobe’s implementation still has its issues.  Certificate encryption only protects PDFs against unauthorized opening, and Adobe digital signatures have weaknesses in their validation process, which allow documents to be altered without warning recipients.

Ultimately, the best way to verify that a document has not been tampered with is to enforce editing and copying controls that users cannot bypass.

  How to lock a PDF from editing online with SmallPDF

If you don’t want to pay for Acrobat Pro licensing, you can use SmallPDF’s online PDF locking tool.  This has some advantages and disadvantages.

The method SmallPDF recommends to lock an editable PDF online involves converting the document to a JPG and then back into a PDF.  This way, rather than a selectable or editable document, the recipient receives a series of images in a PDF document.  Visually, they look identical, but the images are more difficult for someone to edit.  It’s a common method to lock a PDF form and form fields or lock a PDF after signing.

Flattening PDF pages into images is also a common way to lock a PDF from copying since it’s assumed users can’t select the text in an image. It’s worth noting, however, that editing an image-based PDF may not be as difficult as you think.  Tools like Adobe Reader, Foxit, and other PDF editing software come bundled with OCR software that allows them to recognise text in images and make it editable.  They can even bulk convert all the pages to an editable format, undoing your hard work. Other applications, such as Google Lens, let users copy and paste text from any image.

Online tools also require uploading your documents to the provider’s servers, which may come with compliance and security issues in itself. Additionally, your locked PDF documents will be much larger because storing data as images is less efficient.  The ability to search text and click on links (such as the Table of Contents and other links) will naturally break, too.

Just like PDF password protection, then, this isn’t ideal in a business environment.  You can, at least, combine both methods, which will slow an attacker down further, but the system is not exactly foolproof.

How to lock a PDF from editing and copying online:

1. Go to the PDF to JPG converter and drag and drop your PDF file.
   

2. Tick “Convert entire pages” and press “Choose option”.
   
3. Wait for SmallPDF to convert the document.
   
   If you have a large document, this may take some time.  It could be five to ten minutes if you have many pages.  Another downside of this method.

4. Click “Continue in: JPG to PDF”.
   
5. Press “Convert” in the top bar and wait for the PDF to process again.
   
6. Download the PDF and switch to “Protect PDF” via the “Tools” menu.
   
7. Drag and drop your file into the box.
   
8. Enter a secure password and press “Encrypt PDF“.
   
9. Press “Download” to retrieve your protected PDF file.
   

  How to lock a PDF from printing

Applying print restrictions to a PDF document can be a useful way of controlling and securing confidentiality within a document. You can use print restrictions to limit both the sharing of printed copies and the use of printing to bypass other document controls. A common bypass for editing and sharing restrictions, for example, is to print a PDF, scan it back in, and then run it through an OCR tool.

How to lock a PDF from printing with Adobe password restrictions

You can lock a PDF from printing using the basic Adobe password security mentioned earlier:

1. Press the security icon and select “Advanced Options” in the top bar.
2. Select “Password Security” in the dropdown.
   
3. In the resulting pop-up, tick “Restrict editing and printing of the document”. You can then decide whether to disable printing or allow only low-resolution prints. You should also untick “Enable copying of text, images, and other content” to prevent users from copy-pasting into a new document and printing that.
   
   Enter a password and press “OK” to apply the changes.

Naturally, as this method uses Adobe PDF password protection,  it has the same inherent flaws. Users can easily bypass print protection by uploading the document to a free online password remover or by screenshotting the document and printing the images.

To effectively lock a PDF to prevent printing, you’ll need to use a tool that does not rely on passwords or the Adobe Security Handler.

  How do you lock a PDF securely without passwords?

As we established, Adobe Acrobat’s password protection, or any PDF protection system that uses passwords, isn’t a secure way to lock a PDF document.  Not only can passwords be shared or removed, restrictions to stop editing, printing, etc. can be instantly removed by using free PDF password recovery software.

So, how do you lock a PDF securely?  Short answer: you’ll need a PDF DRM solution like Locklizard.  Locklizard trades passwords for a transparent public key system (there are no passwords, keys or certificates to enter or manage) with secure, government-grade encryption.  When you lock a PDF document with Locklizard PDF Security software, it is automatically made read only and is protected from:

• Editing
• Copying (and pasting into other applications)
• Printing
• Screen grabbing
• Saving (as unprotected PDF files)

PDF restrictions are always enforced and cannot be removed using password recovery software or other cracking applications.

If you want to enable printing, Locklizard automatically prevent users printing to PDF files and other unprotected file formats since this is an easy way to unlock PDF documents.  You can also add a dynamic watermark to printed copies to identify the user that made the printouts.  This will discourage users from sharing them with others.

Watermarks can also be applied to viewed content and you can display different watermarks on viewed and printed content.  Unlike Adobe watermarks, Locklizard watermarks are permanent and cannot be removed using PDF editing software.

  How to lock a PDF from editing without passwords

Below is a quick guide to locking a PDF with Locklizard Safeguard PDF Security – controlling who can open it and restricting what they can do with it.

1. 1. Right-click on your PDF and select “Make secure PDF”.
      
   2. Open the “Document Access” tab and choose “Selected customers”.
      
   3. Choose the DRM controls you want to enforce.
      
      Click on the Tabs to select the DRM controls you want to apply. PDF files are automatically locked from editing, copying, printing and screen grabbing.  If you want to enable printing then you can do this from the Printing & Viewing tab. Press the “Publish” button at the bottom of the dialog to lock the PDF file.
   4. Login to Safeguard Admin to grant a user access to the document.
      
   5. Open the “Customers” tab and press “Add” in the sidebar.
      
   6. Enter the user information and click on the “Set Document Access” link in the “Manage Access” section.
      
   7. Select your document and press “OK”.
      
   8. Press the “Add” button on the customer account.  Keep the “Email license” checkbox checked to have the license file emailed to the user’s email address that you have entered.

   Once a user downloads the secure PDF Viewer and clicks on the license link, they can view any PDF documents you have authorized them to use.

   Allowing a user access to the document will allow them to view it, but won’t overwrite any editing, printing, watermarking, or expiry controls you added.  Once a user account has been created you can give them access to any new documents you protect or ones that have already been protected.

   Because Locklizard does not use passwords to protect PDF files, you can lock a PDF from opening and ensure only those users you grant access to can open it.  Even if the locked PDF file is shared with others, only those authorized will be able to open it.  There are no passwords or keys that users can distribute to others, and PDF files are locked to individual machines or devices.

  Locking PDF form fields & signatures without passwords

If you want to lock form fields so they cannot be modified or lock a PDF form after filling it out, then you just use the same process as above.

Any PDF you lock that has a form in it will automatically be protected – users cannot modify form fields and form data can be encrypted on submission so that it cannot be altered unless someone has the correct key to decrypt it.

The same applies if you want to lock a PDF after signing.  After encrypting it with Locklizard, nobody can modify your signature or the document.

  Locking a PDF file to a machine or device

It is possible to lock a PDF file so it cannot be shared by using machine or device locking.

Locklizard automatically lock PDF files to devices.  This stops users sharing PDF documents with others because they have to make the effort to share the physical device (laptop, iPad, etc.) rather than a digital file which can be easily distributed.

Locklizard achieves this by using encryption and a licensing system.  When a user registers their license, the keystore is locked to their device – the keystore holds the decryption keys which are used to unlock PDF files that users are authorized to view.  If the keystore is copied to another device, it cannot be decrypted and so the keys within it cannot be accessed.

This is why an installed PDF Viewer is much more secure than browser-based PDF Viewers (such as those used by secure data rooms) which allow users to login from any device and share their login information with others – because the Secure PDF Viewer has full access to the system it can securely lock the keystore to the device and therefore any PDF documents to it.

  How to lock a PDF by IP address

To be sure that a document or documents aren’t used outside your internal network, you may want to lock them to certain IP address ranges.  You can do this at a global level (for all users) and/or on a user basis.  For example, you might want to prevent all users opening locked PDF files outside the office but let a specific user do this.

  How to globally lock PDFs to an IP address range

A global IP restriction will affect all the users that can open your locked PDF files.  This is useful if you don’t want a document viewed outside of your organization or library.

This can be used in conjunction with the Restrict IP address option on each user’s account.

1. Open the “Settings” tab and click “Restrict IP” in the sidebar.
   
2. Enter your IP addresses or IP address ranges in the “Restrict IP” field.  You have several options for specifying ranges:
   • Wildcard format: 34.567.*
   • CIDR format: 34.567/24
   • Start-End format: 34.567.0-12.34.567.255

   You can add multiple IP addresses or IP address ranges by specifying them in a comma-separated list.  For example:

   12.34.567.8, 12.34.567.9, 98.76.543.*
   
   Press the “Save” button for the changes to take effect.

  How to lock a PDF to an IP for a specific user

As well as global IP restrictions, you can set an IP address or IP address range for individual users.  You can use this in combination with a global IP restriction to ensure that a document can’t be viewed outside of a customer’s department in addition to the organization.  Here’s how:

1. Open the “Customers” tab in Safeguard Admin.
   
2. Press the “Details” arrows next to the user’s name.
   
3. Enter the user’s IP address manually or select “Auto Detect & Restrict”.
   

Scrolling down to the “Restrict Location” section, you’ll notice fields to manually specify the IP address and country or auto-detect and restrict the location.  As with global IP restrictions, you have several options for IP formatting.

If you choose “Auto Detect & Restrict”, the system will automatically record the user’s IP address when they register their license and store it in the IP address field.  This option will add to whatever is already in the field, rather than replace it, so you can safely use both.

Once you’ve entered the relevant IP addresses, press “Save” at the bottom of the window.

  Key takeways for how to lock a PDF securely

1. Password-based PDF Protection is completely useless

   • Using passwords to lock PDFs is insecure, as passwords can be easily shared or removed.
   • Restrictions to disable copy, print and editing can be instantly removed.
   • Passwords can be time-consuming to manage, and challenging to distribute securely.

2. Online PDF Locking Tools provide weak security

   • Online tools like SmallPDF may visually lock PDFs from editing but are not foolproof, as image-based PDFs can still be edited using OCR tools.
   • Online tools still use passwords to lock PDFs from unauthorized access and restrict use.
   • Uploading documents to third-party servers poses compliance and security concerns.

3. Cloud-based systems that claim to lock PDFs from sharing have multiple failures

   • Users can share login credentials.
   • PDFs are not locked to devices.
   • Downloaded PDFs either have no security, dangerous JavaScript, or weak password protection.
   • Users can bypass restrictions by using plugins or scripts – see Google Docs security.

4. Secure PDF Locking without passwords

   • Locklizard provides a secure DRM solution without passwords, using transparent key systems, secure Viewers, and AES encryption.
   • PDFs locked with Locklizard are protected from unauthorized access, editing, copying, printing, and screen grabbing.
   • Dynamic non-removable watermarks deter sharing of photos and printouts.
   • PDFs can be set to expire on a date or after a period of use, and instantly revoked.
   • PDFs are locked to machines or devices, preventing easy sharing, and maintaining secure distribution.
   • PDFs can be locked to country and IP addresses to restrict access outside designated networks.
   • A dedicated Viewer ensures both user-friendliness and maximum security for online and offline files.

  What is the best PDF Locking software?

The best way to lock a PDF

As you can see, the answer to how to lock a PDF file so it cannot be edited, copied, printed, or shared isn’t as simple as it might seem.  Though there are various PDF protection tools or software, many of them are completely ineffective and rely on outdated, password-based systems.  The same is true of secure data room systems that enable users to share login information with others.

Some PDF security or DRM systems force users to make their computers or devices less secure by enabling JavaScript in their PDF Reader or disabling security functionality to allow their plugins to work.  These types of systems should be avoided at all cost – if a user opens a malicious PDF file and their system is compromised as a result of them lowering their security just to open your documents, then you are liable to being sued.

For the best protection, organisations should instead consider PDF DRM software that uses a dedicated and secure PDF Viewer to enforce DRM controls and lock PDF files to devices.  Locklizard provides the ability to lock PDF files quickly and effectively while granting additional printing, viewing, non-removable watermarks, expiry, screen grabbing prevention, and IP restriction controls.  You can revoke access to locked PDF files at any time, regardless of their location, and track how PDF documents are being used.  Users cannot convert locked PDF to Word docs or other file formats, or save them as unprotected PDFs.

If you want to lock a PDF from opening, or lock PDF files so they cannot be edited then take a 15 free day trial of our PDF DRM software.

   FAQs

What is a PDF lock?

A PDF lock is software that locks PDF files or documents from unauthorized access, copying, editing and printing.  A PDF may be locked using:

1. a password – this is not secure since the password can be shared or removed, and permissions or restrictions can be instantly removed using free cloud-based software.
2. transparent key encryption – this is very secure since the user does not enter a password and therefore cannot share or remove it.

Are cloud-based solutions effective for locking PDFs?

No.  Not only do they rely on passwords for authentication (which can be shared), they also rely on JavaScript to enforce restrictions.  JavaScript can be disabled in the browser or modified to bypass copying and editing restrictions.  Good examples of this are Google Docs security and Docsend2PDF.

In addition, because they have no control over the browser environment, they can’t prevent screenshots, printing to PDF, or effectively control sharing of downloadable files.

How can I make a PDF file read-only and prevent editing, copying, and printing?

To make a PDF file read-only and prevent editing, copying, and printing, you can lock the file using PDF DRM software.  This will prevent users from sharing, modifiying, printing or copying the content.

While you can prevent editing and printing using passwords, the protection is simple to remove and therefore worthless.

What is the least secure method of locking a PDF file?

Using a password to lock a PDF file is one of the least secure methods.  Authorized users can share locked PDFs and the password with others or simply just remove it.  Free online cracking tools can remove any printing and editing restrictions instantly.

How can I lock a PDF file with a password?

You can use Adobe Acrobat or any other PDF editor to lock a PDF with a password.  However it is pointless to do so unless you trust the recipient not to share it with others.  You must also use a strong password to lock the PDF file, otherwise password removal tools will easily crack it.

Can I lock a PDF file with a certificate to restrict editing?

You can, but it is no more effective than locking a PDF with a password to restrict editing.  Authorized users can decrypt the locked PDF and then use a free online PDF password removal site to remove editing restrictions.  Note also that permissions or restrictions are not honored by all PDF viewer or reader apps to begin with.

Why choose Locklizard to lock PDF files from copying?

If you want effective restrictions to lock PDFs from editing, copying and sharing, then only dedicated installed Viewers can achieve this.  When you lock a PDF using Safeguard, it creates an encrypted PDF with DRM restrictions that not only prevents unauthorized access, but disables any attempts at copying or editing.  Locked PDFs can only be opened in our secure PDF readers which disable copy functionality – copy and paste, screenshots, prints (and printing to file drivers if printing is enabled) and modifying of PDFs are all blocked.

Encrypted PDF files are locked to devices so they cannot be shared, and unauthorized access is prevented by the use of secure licensing controls and transparent key management (there are no passwords for users to enter or share with others).  Unlike password protected PDFs, users cannot share passwords with others, or remove permissions using Mac Preview, free online tools or similar workarounds.

Our secure Viewer software is available for Microsoft Windows, Mac, iOS and Android platforms, offering a user-friendly experience while ensuring maximum security for both online and offline (downloaded) files.