I've recently switched to Linux and I'm looking for a way to verify PDF signatures. In Windows, I always used Adobe Reader for this, but I'm not sure what to use now. I heard about OKular being capable of verifying signatures, but it doesn't seem to do it automatically when I open a PDF. Can someone explain how I can verify signatures using OKular? Additionally, I'd love to understand how PDF signature verification actually works.
4 Answers
In OKular, signatures should show up automatically when you open a PDF. If it isn’t, check the documentation to make sure everything is set up right. There’s a section about adding digital signatures which might help you troubleshoot the issue.
You should definitely check out Qoppa Software's PDF Studio Reader. I've found it to be the best free PDF reader for Linux. I once had an issue while using the free version, and when I contacted their support, they responded super quickly and even fixed the problem! They may not be open-source, but they're super friendly towards the Linux community. If you like it, consider buying the full edition; it goes on sale for pretty cheap sometimes.
PDF signature verification works using asymmetric cryptography. Basically, when a file is signed, a hash is created from it and then encrypted with the signer’s private key. When you want to verify the signature, you decrypt it with the signer's public key and compare the result to a newly computed hash of the PDF. If they match, the file is intact and signed by the legitimate owner. OKular does all of this for you, but be cautious about the public key you’re using.
You can still use Adobe Reader on Linux, but just be aware that it's quite outdated, being a 12-year-old version. There are better options out there now!
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