How to encrypt PDF files for free

Yesterday I wrote about the importance of encrypting documents before you send them via e-mail. But what if you don’t have a PDF creator, other than Microsoft Office or Open/Libre Office?

It turns out you can encrypt PDF documents, including those you create with office software, for free–with caveats.

The software to do it is called Pdftk (PDF Toolkit), which you can download from here. The downsides are that it’s a command-line program–though Wikipedia provides links to several GUI front-ends if the command line is too off-putting–and that, as far as I can tell, it only supports the obsolete RC4 encryption method. Yes, it’s 128-bit, but 128-bit RC4 is far easier to crack than 128-bit AES. Not all 128-bit encryption is created equal.

To me, this is a solution of last resort. Zipping the files using AES encryption is better, and 7-Zip will do it for free, and with a GUI. If you’re sending a file to someone and the best they can do is PDF–maybe they don’t have a decent Zip tool on their machine and don’t have the rights to install one–then 128-bit RC4 is much better than sending it unencrypted. But I wouldn’t be happy about it.

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