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Often, I receive PDF documents that make use of Adobe Acrobat's functionality for digital signatures.

I can sign those PDFs with a self-signed certificate, but then Adobe Acrobat Reader shows a warning sign that the signature is untrusted.

Where can I buy a personal digital certificate that would allow me to sign PDF documents, so that the signature can be validated with the default root certificates in Adobe Acrobat reader?

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I suggest that you use D-TRUST, since it is a German provider (your country), it is listed in Adobe Approved trust list and it is installed as trusted root certificate in Windows.

Basically I suggest to follow theese rules:

  • use local certificate authority that provides digital signature certificates that are legally valid in your country
  • use personal digital signature certificate that is linked with your name (they can also offer system certificates etc.)
  • use a certification authority that uses pre-installed root certificate - check Adobe Approved trust list and Windows Cert Store.

You can check Adobe trusted root authorities directly in Adobe Reader here (only Czech language...): Settings - Signatures - Identities and trusted certificates - ...

Settings

Trusted

In Windows check this - but Windows trusted certificates must not be automatically trusted by AR, check this thread:

Windows Cert Store

  • I don't think the Windows root certificates apply. I have a code signing certificate installed on my Windows machine that is valid and I can use it to sign PDF files, but Acrobat shows the signature as untrusted. – Ingo Kegel Jun 23 '15 at 8:20
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    I see, it used to be so, but it has probably changed with AR X version... – Vojtěch Dohnal Jun 23 '15 at 8:32
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    It has to be setup explicitly now... forums.adobe.com/thread/1731839 – Vojtěch Dohnal Jun 23 '15 at 8:32
  • Interesting. The question remains what kind of certificate Adobe wants me to by so that other people will see it as trusted. – Ingo Kegel Jun 23 '15 at 9:44
  • @IngoKegel Those root certificates and also your signature certificate will be periodically updated, so it also depends on a mechanism, how updates to pre-installed root certificates work. Windows update works quite OK I would say, not sure about Adobe. – Vojtěch Dohnal Jun 23 '15 at 9:58
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There is a way to mark your certificate as trusted. Read this adobe help page. It basically explains everything about certificates, including how to validate your certificate. Even though you might be limited to make certificates "trusted" only in your machine.
Some other articles I suggest:
About Certificate signatures | Digital signatures, Adobe Approved Trust List
In case you want to buy a personal certificate, check out these pages:
http://www.entrust.net/adobe-cds-certificates.htm
https://www.globalsign.com/en/personalsign/ (this one could be what you are searching for)

Read also the list of all Adobe Approved Trust List members, to choose the desired company where to buy a personal certificate.

  • I'm not interested in making it appear trusted on my machine, I want the person who sent the PDF to me to see it as trusted when I send it back to them. I don't see anything on the globalsign web site regarding PDF documents in Adobe Acrobat. – Ingo Kegel Jun 23 '15 at 8:23
  • I edited the question. According to that adobe page, globalsign is a trusted member. So buying a certificate for your personal sign will be seen as trusted everywhere if you buy it from them or any of the list provided by adobe. – Erlis D. Jun 23 '15 at 14:25

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