Does anybody know how to validate digital signature on Linux previously i used Adobe Reader DC on Windows. I'm Unable validate the Digital signature using Default app "Document Viewer". is there any alternative apps.
Please help!! It's urgent
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I think LibreOffice lets you validate digital signature, I'm not sure because I never did it.
In
LibreOffice Draw:
File → Digital Signatures → Digital Signatures
You can use other software if you want to, it just comes to personal preference. I'm just showing LibreOffice Draw because it's preinstalled.
Maybe others in the forum can recommend other software!!! 
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@Aravisian @FrenchPress, I don't know any software to sign PDFs, I don't want to recommend something I never used before.
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Is this help?
For GUI way, you need Master PDF.
Download the previous version 4 from here.
The latest version 5 stripped much functions from the free version.
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Nothing working. That Master PDF worked but it not allow me to save. maybe bcz it's not register. Anyway Thank you all for help.
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@asr
There are 3 different versions on that page.
Which one you downloaded?
I just tested on my copy of Master PDF.
It is version 4.3.89 based on QT5.4.1, 64 bit
unregistered version
and I can save all edits I made.
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master-pdf-editor-4.3.89_qt4.amd64.tar.gz
are talking about this version then its not even opening
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You should download this:
http://code-industry.net/public/master-pdf-editor-4.3.89_qt5.amd64.deb
That is a source. You need it only when you have to compile it for Linux distro which does not use neither .deb nor .rpm
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btw chrome saying its not safe file, do want me to continue
using chrome?
It works now, I use Chromium
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It is where I downloaded it from and I had no ill effects.
is a reputable sites and their tutorials are trust worthy.
I use Firefox and getting absolutely no warning for downloading files from that link.
Keep it, and use your terminal to install
sudo dpkg -i master-pdf-editor-4.3.89_qt5.amd64.deb
I also get warned, but I trust you to not send malware to this thread.
Your love for terminal command showing again 
OP can just double click on the downloaded file to install.
That will use the software GUI, which is basically a candy store, and it's slow. I deleted it
not working. previously i can click on info then valid signature but now info button is black out