Digital signatures and PDF are an increasingly popular combination for digitizing paper-based business processes. While the focus of most signature products and solutions is on the creation of the signature itself, the correct validation of signatures contained in PDF is somewhat pushed into the background. Signature validation is a greater challenge for software development than signature creation. The presentation uses a series of practical examples to show how signature validation is presented to the user, what expectations he has of it, and what difficulties and problems can arise during validation. Especially since the publication of attack scenarios on signed PDF documents, questions about correct validation are becoming increasingly important.