Locking a single PDF from being opened takes just a few seconds. You simply set a password and, when applicable, select your level of encryption, then save the file. Password protection has been around for decades, and it’s still the most common way to protect files on a workstation or home computer. If you want to share a file with others or protect multiple documents, however, passwords can present problems. 

Locking PDF Documents With a Password

The most common way to protect a PDF document from being opened by unauthorized users is to encrypt the file and set a password. This can be done with most of the software you would use for creating or editing a PDF file, including Microsoft Office, Adobe and Apple Preview. 

How To Lock a PDF in Microsoft Office

If you’re creating a PDF from a Microsoft Office document, you can lock it during the export process. When you’ve finished editing your document and are ready to export it, select File > Export. In the Export window, select the “Create PDF/XPS Document” option to create a PDF. 

When the Save dialog box opens, click the “Options” button. Next, click “Encrypt the document with a password” at the bottom of the Options window, and then click “OK.” You will then be prompted to enter a password. To open the encrypted PDF, you or anyone else will need to enter that password. 

How To Lock a PDF in macOS

Preview is the default software on Mac computers for opening, editing and configuring PDF files. To lock a PDF in macOS, open it in Preview. To do this, you can right-click the file in Finder and select “Preview.”

Select File > Export. In the Export window, once you select “PDF” from the Format menu, you will see an “Encrypt” button appear. Select it, enter a password and verify it. If you save the file with the same name in the same folder as the original, this will overwrite the unencrypted version. Otherwise, saving it to a new folder or choosing a different name will give you a new, encrypted version of the original.

Disabling encryption and password protection is just as easy. Simply use the Export option again and then turn off the encryption option. Because this is so easy, keep in mind that anyone with the password also has the ability to disable its security. 

How To Lock a PDF With Adobe Software

Adobe offers a free online tool for adding security to PDF files. Simply navigate to Adobe’s password protection page and drag a PDF into the drop zone. After you enter a password and confirm it, the file will be encrypted and you will be prompted to download it. You will need to enter the password whenever you wish to open the encrypted file.

If you’re using Adobe Acrobat, you can use that to lock your PDFs as well. In Acrobat, select Tools > Protect > Encrypt > Encrypt with Password. Enter a password and select the compatibility level. Older versions of Adobe Acrobat are not compatible with the latest encryption methods. For the best encryption, select Acrobat X and later.

Types of PDF-Locking Protection

There are several different ways of locking a PDF file, depending on your needs. 

  • Printing: You can prevent users from printing a PDF, or limit the number of times they can print it. 
  • Editing: You can allow others to view the PDF but not edit it. You can also allow them to edit specific portions of a PDF but not others, which is a valuable feature when you need someone to fill out a form. 
  • Expiration date: You can set a PDF to be unusable after a specific date. After that date, the document can no longer be opened, even if a copy has been downloaded to the user’s computer. 
  • Dynamic watermarks: A digital watermark appears on each page of the PDF when it is printed or downloaded. The information in the watermark identifies who downloaded or printed the document. 
  • Access monitoring: Each time a person accesses a document, the event is recorded in an activity log. Reviewing the log, you can determine when it was viewed and by whom, as well as if it was edited, downloaded or printed by the user.
  • Authorized devices: PDF files can be locked from access by unauthorized devices. 
  • Authorized locations: PDFs can be locked to specific places using IP address ranges. Anyone outside of a specified IP address, or a range of addresses for a country or region, will be unable to access the document.
  • Print-screen protection: Locked PDFs can prevent anyone from using print-screen or screen-capture software from saving a snapshot of an open document.

How To Lock a PDF From Editing

If you want anyone to be able to view a PDF but do not want them to have the ability to edit it, you will need a specialized tool, like the one available in Adobe Acrobat Pro DC. This is premium software, but you can get a free trial from Adobe. Once you have opened the PDF, select Tools > Protect and then choose the option to restrict editing with a password. That same list of options also allows you to encrypt the document. Once you choose a password, only those with the password can make changes to the document. 

Encryption and PDF Security

Encryption technology continues to evolve. According to the US Department of the Treasury, modern Adobe PDFs using Acrobat X and later (PDF 1.7) support 256-bit AES encryption. Adobe Acrobat 7 (PDF 1.6) supports 128-bit AES encryption, and Acrobat 6 (PDF 1.5) supports only 128-bit RC4 encryption. 

While 256-bit AES encryption is the best of these three choices, it’s important to point out that even 128-bit AES encryption is still pretty good today. Hacker Noon estimates that it would take a modern computer up to 500 million years to crack a 128-bit encryption key.

Passwords: Security’s Achilles’ Heel

Using the best, most complicated method of encryption is absolutely worthless if someone can guess your password. It’s even worse when you give someone your password. 

Password-protected PDF files are designed to keep your documents secure only if nobody knows your password. The moment you share that password with someone else, like a client, a consultant or a co-worker, they have the power to do anything they would like with your document. This includes disabling the password and permanently unlocking the document.

How To Lock Multiple PDFs at Once

Another disadvantage of password-secured PDFs is that you have to set the password for each document one at a time. This becomes time-consuming if you have a couple dozen documents, let alone several hundred. 

This document-level security also raises the question of how many passwords you will use. If you protect them all with the same password, and then share those documents with different groups of people, the passwords become close to useless. On the other hand, using a separate password for each of 100 or 1,000 documents becomes a logistical nightmare.

If you have multiple files that need to be shared, folder-level security is much more efficient and secure than document-level security. A virtual data room (VDR) is designed to lock thousands of documents at once, which can be uploaded and automatically encrypted in bulk.

Protecting PDFs in a VDR

Using a VDR like CapLinked is the most efficient and secure way to share PDF files. Within a single workspace, you can create multiple folders for different types of documents and then grant specific types of permissions to different groups of people. Your team, for example, may all have the ability to upload and edit documents, while clients or investors have only read-only access to the contents of specific folders, with security restrictions such as:

  • Time-limited viewing access
  • Digital watermarking of all downloads with IP address, email address and a time-stamp
  • Download restrictions
  • Printing restrictions
  • Revocation of access at any time, including downloaded documents

Documents are encrypted using military-grade 256-bit encryption and are stored on servers that are SSAE18 and ISO 27001 certified. Setting all of this up takes only 10 or 15 minutes, depending on how many different types of group permissions you want to use. To explore these features for yourself, sign up for a free trial. 

David Weedmark is a published author and e-commerce consultant. He is an experienced JavaScript developer and a former network-security consultant.



Adobe: Password Protection Page

Apple: Password-protect a PDF in Preview on Mac

US Treasury: How to Encrypt/Password Protect Microsoft Office and Adobe Acrobat (pdf) Documents

Adobe: How to Password Protect PDF Files 

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