Saves a copy of the PDF file that is covered by this signature.
The stream used to create the object from which this signature was retrieved is required as input because the document does not keep a reference to the stream it was created from. Because the digital signatures are computed on the physical layout of the PDF file, it is impossible to recreate this layout from a loaded object.

public void saveSignedCopy( 
   Stream signedFile,
   Stream output
)