Adobe is a U.S. American software provider that can display PDF documents with its widespread product Adobe Acrobat Reader. This program allows the verification of certificate-based electronic signatures. Whether a signature is valid and receives the green check depends on many aspects, e.g.:
- Adobe has its rules, classifying issuing certification authorities of trust service or certification service providers as "trustworthy". These providers are listed in the Adobe Trust List (AATL). Swisscom always endeavors to get listed, even if not included in the service description. In addition, the listed companies pay annual fees for the entry and hand in a self-assessment. According to Adobe, certified trust service providers, according to EU regulations, eIDAS is considered trustworthy if they have concluded a contract with Adobe.
- Adobe offers a variety of settings that can lead to a different validation: For example, instead of Adobe's trust list, you could use the trust list of Microsoft, which usually maintains trust service providers that issue SSL or e-mail certificates. However, the check can be based on a time given by the computer clock and not on the electronic time stamp in the document.
In conclusion, you can only rely partially on the validity of signatures in Adobe. Though, you might get details about the signature's certificate and information if document changes have been made after the signature had been placed.