There are currently two values (bit positions) for the SigFlags key defined:
1 - SignaturesExists
2 - AppendOnly
I got questions regarding the signing state of a signature:
I) SignatureExists Bit position means that there are unsigned/empty signature fields?
II) AppendOnly Bit position means that there is at least one signed signature (which would be invalided if changed "normally"). Or can the AppendOnly mode also be used to indicate that I (as a document creator) want that all changes are done in appand mode?
III) Those values are bit values which can have the following value in the final PDF:
0 - nothing set
1 - SignatureExists=true, (AppendOnly=false) - Signed or unsigned signature exists
2 - AppendOnly=true, (SignatureExists=false) - All changes should be done in append mode, don't know whether there are signatures
3 - SignatureExists=true, AppendOnly=true - There are signatures all changes should be done in appendMode
@Leonard - Any hints?
Those are indeed the only values for SigFlags. And your statements about the values are 100% correct.
If bit 1 (HasSigs) is set, then the document has signature fields. They may be *either* signed or unsigned
if bit 2 (AppendOnly) is set, then any changes to the PDF *shall* be done in append mode. By itself, not an indication of signed fields.
If *both* bits are set, then the file has signed fields.