Different document write modes.
Instead of appending an update only, the document is completely rewitten. Note that existing signed signature fields will be invalidated.
The document is writen eighter Full or AppendUpdate, depending if a signed signature is already embedded in the document or the document is marked that it allows to have updates only. New document will be written in Compact mode. Existing document will be written in Full mode if possible, otherwise AppendUpdate mode will be used.