PDF encryption upon export from Preview

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PDF encryption upon export from Preview

I want to apply secure (say, 128-bit) encryption to a PDF file before emailing it. According to various sources, the Export/PDF option in Preview will allow one to apply some sort of encryption and also password protection. The password protection seems to work, but I can’t tell whether the file itself is encrypted. I expected any encryption to significantly reduce the file size (as happens when using zip -e from Terminal) ... but it doesn’t. Does anyone know what Preview is doing or how to verify that the output PDF is indeed encrypted and at what level?

iMac Line (2012 and Later)

Posted on Oct 5, 2019 4:31 PM

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Answer 1

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VikingOSX

Level 10

123,566 points

Oct 6, 2019 4:42 AM in response to guyfromtx

When you export a PDF from Preview in Mojave 10.14.6 (18G103), it is encrypted as 128-bit AES. Neither Preview's Inspector, nor the Finder's Get Info will tell you the level of encryption. You will need to open the PDF in Adobe Acrobat Reader DC (v2019.*), and from the Edit menu, select Protection > Security Properties, which will open a general panel. On that panel is a Details… button that shows the encryption level.

Some PDF Editors (e.g. Master PDF Editor, PDFPenPro) offer higher levels of encryption (e.g. 256-bit AES) with reduced opening application compatibility.

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Answer 2

Barney-15E

Level 10

122,420 points

Oct 6, 2019 3:52 AM in response to guyfromtx

Why would you suppose that encryption would reduce file size?

To encrypt it, you would need to obfuscate its content. That would more than likely increase the file size, not reduce it.

If all the encryption did was substitute bytes or other bytes, it could easily be broken.

I don't know how to confirm that it is actually encrypted.

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PDF encryption upon export from Preview

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