Tutorial by Examples

You want to add a signature to a PDF in a way that a standard conform PDF viewer (e.g. Adobe Reader) will recognize, display, and validate as an integrated PDF signature. In that case you cannot simply externally create a signature covering the original PDF as is and expect to now have to merely so...

If multiple signatures are to be integrated into a PDF, this is done by means of incremental PDF updates (explicitly not by adding multiple SignerInfo structures to a single integrated CMS signature container!): The cryptographic verification of these signatures merely guarantees that the byte ra...

A PDF document may contain the following standard types of signatures: Any number of approval signatures in signature form fields. At most one certification signature in a signature form field. It enables the author to specify what changes shall be permitted to be made to the document and what c...

In the Adobe technical white paper Adobe Acrobat 9 Digital Signatures, Changes and Improvements, especially its section "Allowed and disallowed changes", Adobe clarifies the allowed changes (as seen by Acrobat 9 and up) that can be made to a certified or signed document without invalidatin...

The specification says: A byte range digest shall be computed over a range of bytes in the file, that shall be indicated by the ByteRange entry in the signature dictionary. This range should be the entire file, including the signature dictionary but excluding the signature value itself (the Conte...

As the header already says, the following list contains "interoperable signature types" which are more or less strictly defined. The PDF specification specifies a way to also include completely custom signing schemes. But let us assume we are in an interoperable situation. The the collecti...