In order to send a file securely, I am going to encrypt/password protect a PDF file with Preview on macOS.

Other question(s), such as this one have asked the method of encryption for PDF's in general, but not about Preview on macOS specifically. I learned from that question that Adobe Acrobat uses very secure encryption methods, but I am unsure how Preview on macOS handles this.

I am on macOS 10.12.6. I am encrypting a PDF by going to File>Export>Encrypt in Preview.app.

This is similar to my other question here.


1 Answer 1


Part of the PDF specification describes the encryption of PDF data, and Preview produces a 'to-spec' encrypted PDF.

Encrypted PDFs made by Preview are valid PDFs that can be opened (when the password is provided) by any PDF app that follows the spec on any platform.

The level of encryption depends on the PDF version.

Early versions of MacOS saved with PDF v1.4, giving RCA-128bit encryptions. Newer versions save as PDF v1.6, giving AES-128 encryption. You can see the version level of the PDF document in Get Info.

preview info encryption

Source: https://apple.stackexchange.com/a/400693/88907

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