Digitally sign PDF-documents
Adobe Reader and Acrobat Pro support digital signing of PDF documents. However, there are also reports that there are ways to manipulate these documents so that fake content is displayed as authentic by various PDF readers.
Therefore, trust signatures embedded in PDF files with caution.
In important cases, it is better to use an external signature, e.g. by sending PDF documents in digitally signed e-mails.
Before first use: Install root certificate
Since the root certificate is not automatically known in Adobe Reader, it must be imported before the first use so that digital signatures with the HZB (e-mail) certificates are considered valid for signed PDF documents.
To do this, first save the root certificate to a file locally on your device so that you can import it into Adobe Reader. (Download root certificate)
Now open Adobe Reader and select "Settings" in the "Edit" menu.
In the "Signatures" category, in the "Identities and trusted certificates" section, select the "More..." button.
Select "Trusted certificates" and then click the blue arrow to import.
Click "Browse" and select the root certificate file stored on your computer.
Mark the root certificate with the name "T-TeleSec GlobalRoot Class 2", it now appears in the lower area of the window. Click "Import".
The root certificate is now imported but not yet known to Adobe Reader as trusted. Mark the certificate "T-TeleSec GlobalRoot Class 2" in the list and click the pencil icon.
Check the box "Use this certifcate as trusted root" and further down for the purpose "Certified documents". The other 3 checkboxes remain empty, as the HZB e-mail certificates are not suitable for these purposes.
Click "OK" and close the windows.
Digitally sign a PDF document
To digitally sign a PDF document with your email certificate, open the file in Adobe Reader or Acrobat Pro. Click "Tools".
Now click on "Sign digitally". Close the message window that may appear by clicking "OK".
Then, click and drag the mouse to draw a rectangle at the location in the document where you want the digital signature to be displayed.
Now select your digital certificate that you want to use for signing.
Depending on the security level with which you had imported the certificate, you may be asked for the password for your secret key. In that case, enter the password.
Then click on "Sign".
At this time, you must specify a name and location for the signed document. The document is not actually digitally signed until you save it. Afterwards, you will see the appearance of your digital signature at the previously marked location in the document. This is only a visual representation, whose appearance you can also customize. The actual digital signature is invisible.
If you want to view more information about your digital signature, click the insertion.
In the same way, a document can also be provided with additional digital signatures.
Verifying the signature of digitally signed PDF documents
To verify digitally signed PDF documents, you don't actually have to do anything because Adobe Reader and Acrobat Pro automatically indicate whether a document has been digitally signed and whether the signature is valid.
By clicking on "Signature Window" you can see information about all digital signatures of this document.
By expanding the signature field, you can display even more detailed information about the digital signature if required.