I am able to open digitally signed PDF's in Ubuntu and other distributions, but for some reason the GNOME pdf viewer that is default in Zorin doesn't open them. I was able to install Core PDF to open them, but why doesn't the default GNOME PDF viewer work in Zorin?
You can use FoxIt Reader, rather than the built-in PDF reader:
That'll pop up a dialog box, select "64-bit Linux". It's the exact same PDF reader as is used in Windows. It'll save a .tar.gz file (I save it to the Desktop). Extract that then double-click the extracted file to start the installation.
After the installation is done, the icon for FoxIt Reader will be in Zorin menu > Office. Start it up, select Edit > Preferences > File Association and click the Make Default button.
I think it's great that I can use all the same programs under Linux as I used under Windows... FoxIt PDF Reader, SRWare Iron browser, PDFsam pdf manager, LibreOffice office suite, VLC media player, etc.
I do not know the answer, but I suspect it is due to Gnome document Viewer (Evince) having bugs with Poppler. Long, long standing bugs.
As @Mr_Magoo suggested, you can easily work around this with another pdf viewer. Xournal, Foxit, LibreOffice Draw all can manage signed .pdf files and you can sign with them - you can also do this in GIMP (Though you will need to look up a How To Guide on that...)
I don't need foxit, adobe, or any other windows app. I'm just hoping to learn why the gnome pdf viewer in Zorin can't open a digitally signed pdf file when the same gnome app in Ubuntu will open them.
Try opening in Libreoffice Draw.
To my knowledge Google had created it's own code for PDF's, as far as i know this code has never been released.
here's a brief explanation, Old but still relevant.
Note: if you create a pdf with Libreoffice writer, you will be able to re-open it with libreoffice.
Another quick option is to convert the file to excel. this can be done within libreoffice.
Hope this may help.
Perfectly valid. Which edition of Ubuntu did you test it on?
Ubuntu 20.04? 21.10? 22.04?
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Ubuntu 22.04. I have no problem opening with several verisons of Mint Linux either.
Can you try sudo apt-get update and then sudo apt-get install --reinstall evince and let us know if this changes your problem at all?
If the above doesn't help, its possible that a system date/time conflict exists on the machine you're trying to use or a certificate issue might be causing the problem as well.
To automatically synchronize the system clock with remote network time protocols from the internet: sudo timedatectl set-ntp true
Regarding the CA certificates realm of possibility:
Evince can check the authenticity of digitally-signed PDFs using CA certificates. When a PDF is digitally signed, it contains a digital signature that is verified using a public key infrastructure (PKI) based on certificates issued by trusted certificate authorities (CAs).
If the certificate chain is valid and the certificate is trusted, Evince displays a green checkmark indicating that the signature is valid. If the certificate chain is invalid or the certificate is untrusted, Evince displays a red X indicating that the signature is not valid.
If these certificates don't exist, are out of date or are invalid on your Zorin installation; there might be some conflict with the Evince program installed with your OS as it checks the authenticity of the digitally-signed PDF against the system's trust store to determine the certificate chain in the embedded digital signature and checks it for validity/whether it was issued by a trusted CA.
For this, you might try: sudo apt-get install ca-certificates
By installing the ca-certificates package, the system's trusted CA certificates list is updated.
Hope this helps!
You have answered your own question. Zorin 16.2 is based on Ubuntu 20.04. Zorin won't be on 22.04 base until Zorin 17 is released, hopefully, later this year. You could use Okular instead - it is more than just a pdf viewer! I prefer Okular over any other pdf viewer, whether it be in Windows or GNU/Linux. (Okular is also available for Windows).
Doesn't the question of Ubuntu version differences imply that there have actually been changes made to handling of digitally-signed PDFs in Evince, or Ubuntu as a whole, between version 20.04 and 22.04?
Correct. In much the same way 'Document Scanner' improved with Zorin 16.x over 15.
Gotcha. I just wondered because I didn't see anyone pointing out the differences and that those changes were actually made to Ubuntu 22.04 for better handling of digitally-signed PDFs compared to Zorin's 20.04.
I suspect it might have a bearing on packages and the kernel in use.
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