This property allows you to determine if the PDF has been
tampered with after signing.
It is important to understand that certain types of updates are
allowed. The validity of this property relates to the validity of
the particular revision of the document. So it allows you to
determine if the original PDF has been tampered with in any
However it is possible to update PDF by incrementally updating
the revision. This will provide a document which contains
modifications but can be backtracked to show the exact state of the
document at the point that a particular signature was applied.
Most commonly this is needed when multiple signatures are being
applied as each signature needs to be applied to a new revision of
the document and to be valid for that particular revision.
See also the Validate