The three ways to encrypt a PDF depend on what software you already have

You can encrypt a PDF using built-in tools on Windows and Mac, free online converters, or the original software that created the document. The method you choose depends on whether you want to set a password that prevents opening the file, a password that prevents editing or printing, or both. Most PDFs you receive are encrypted with a "user password" — the one you type to open it — but some have an "owner password" that restricts what you can do inside the file even after opening it.

The fastest route is usually your operating system's built-in tools, which work on any PDF without installing anything new. If you need more control over permissions — like allowing someone to view but not print — you may need Adobe Acrobat (the paid version, not the free Reader) or a dedicated encryption tool.

Key Takeaways

  • Windows and Mac both have built-in PDF encryption: right-click the file on Windows and choose "Properties," or use Preview on Mac and select "Encrypt" from the File menu.
  • A user password prevents anyone from opening the PDF without typing it first; an owner password lets the file open but restricts printing, editing, or copying text.
  • Free online PDF tools can encrypt files, but uploading sensitive documents to a website carries a privacy risk — use them only if you trust the service.
  • Adobe Acrobat (paid) gives you the most control, including the ability to set different permissions for different passwords and restrict specific features like form-filling.

Encrypting a PDF on Windows using built-in tools

Windows does not have a native "encrypt PDF" button, but you can password-protect a PDF by opening it in Microsoft Edge (the default browser) and printing it to a new PDF with encryption. Open the PDF in Edge, press Ctrl+P to open the print dialog, select "Print to PDF" from the printer dropdown, click "More settings," and check the box for "Save as PDF with security options." You will then be prompted to set a password before the file is saved.

This method creates a user password — the file cannot be opened without it. If you need an owner password instead (to restrict editing or printing while allowing the file to open freely), you will need Adobe Acrobat or a third-party tool. Windows 11 also allows you to encrypt files using BitLocker, but that protects the entire folder, not individual PDFs.

Encrypting a PDF on Mac using Preview

Mac's Preview app can add a user password to any PDF. Open the PDF in Preview, go to File menu and select "Encrypt PDF," then enter and confirm your password. The encrypted file will be saved with the same name, replacing the original — save a copy first if you need to keep an unencrypted version.

Preview only sets a user password, not an owner password. If you need to restrict printing or editing while allowing the file to open without a password, you will need Adobe Acrobat or an alternative tool. Preview's encryption uses AES-128 bit encryption, which is strong enough for most purposes.

Using Adobe Acrobat to set different passwords for opening and editing

Adobe Acrobat (the paid version, not the free Reader) lets you set both a user password and an owner password, giving you fine-grained control. Open the PDF in Acrobat, go to File > Properties > Security, and choose "Password Security" from the dropdown. You can then set a password to open the document, a password to change permissions, and choose which actions are allowed — printing, editing, copying text, or filling forms.

This is the only method that lets you, for example, allow someone to view and print a document but prevent them from editing it or copying text out. The trade-off is that Adobe Acrobat costs money (around $180 per year for the full version, or $15 per month). If you only need a simple user password, the free Windows or Mac methods are sufficient.

Free online PDF encryption tools and their trade-offs

Websites like ilovepdf.com, smallpdf.com, and pdf2go.com offer free PDF encryption without installing software. You upload the file, set a password, and download the encrypted version. These tools work on any operating system and are fast, but they require you to upload your document to someone else's server, which carries a privacy risk if the document contains sensitive information.

If you use an online tool, choose one that explicitly states it deletes files after a set time (usually one hour) and uses HTTPS encryption for the upload. Read the privacy policy to understand what the company does with your files. For documents containing financial information, medical records, or personal data, the built-in Windows or Mac methods are safer because the encryption happens on your own computer.

What encryption strength means and whether it matters

Most PDF encryption uses either AES-128 or AES-256 bit encryption. AES-128 is strong enough that breaking it would take longer than the document is likely to remain valuable. AES-256 is stronger and is what government agencies use for classified documents, but for most personal or business PDFs, the difference is not practical. The password you choose matters more than the encryption strength — a weak password like "123456" can be cracked quickly regardless of whether the encryption is 128 or 256 bit.

When you set a password, use at least 12 characters mixing uppercase, lowercase, numbers, and symbols. A password manager like Bitwarden or 1Password can generate and store strong passwords so you do not have to remember them.

Removing encryption from a PDF you already own

If you encrypted a PDF yourself and forgot the password, you cannot recover it — encryption is designed to be irreversible. If you have the original unencrypted file, you can re-encrypt it with a new password. If you do not, you will need to recreate the document or contact whoever gave you the file and ask for an unencrypted copy.

If someone else encrypted a PDF and you have the password, you can remove the encryption by opening it, printing it to a new PDF without the security options, or using a tool like qpdf (command-line, free) or Adobe Acrobat to save it unencrypted. Some online tools claim to remove PDF passwords, but many of these are scams — avoid them unless you trust the source.

Frequently Asked Questions

Can I encrypt a PDF that is already encrypted?

Yes. You can open an encrypted PDF (if you know the password), then encrypt it again with a different password using any of the methods above. This is useful if you want to change the password or add an owner password on top of an existing user password.

Does encrypting a PDF make it smaller or larger?

Encryption adds a small amount of overhead, usually less than 1 percent of the file size. The difference is not noticeable for most documents. The file size stays roughly the same.

Can someone open an encrypted PDF on their phone?

Yes, as long as they have a PDF reader app and know the password. Most phones have built-in PDF readers (Apple Books on iPhone, Google Drive on Android) that can open password-protected PDFs. Some third-party apps may not support encrypted PDFs, so test before sending.

What if I encrypt a PDF but forget the password?

You cannot recover a forgotten password — encryption is designed to prevent that. Keep your passwords in a password manager so you do not lose them. If you lose access to the encrypted file, your only option is to recreate the document from the original source.

Is encrypting a PDF the same as digitally signing it?

No. Encryption protects the content from being read or modified. A digital signature verifies who created the document and proves it has not been changed since signing. Some PDFs have both — encryption for privacy and a signature for authenticity.