Returns the part of the document that is covered by the signature.
Use this method to retrieve the revision of the document that is covered by the SigIndex signature.
PDF documents often use incremental updates approach, with any changes being appended to the document without altering the existing revision. This may lead to situations where a signature only covers a part of the document (one of the past revisions), but not the subsequent changes. GetSignedVersion method provides means to extract the revision that is actually certified by the signature.
It is recommended that you use this method when validating signatures to make sure the signature covers what you expect it to cover.
An alternative to this method is to check the CoverageEndsAt field of the signature object and match it to the document length.