Signature layers in 2.0 are incorrect

[Tilman Hausherr <TH...@t-online.de>]

Due to a change in creating resource names in 2.0, the only layer we 
create when signing is "n1". In 1.8, it was n0.

n1 is "very wrong", it is meant to be "Validity layer, used for the 
unknown and valid state".

Using n0 was also wrong all the years, it is the background layer. My 
understanding after reading the text below is that we should create an 
empty n0 layer and put text and image into n2.


https://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/PPKAppearances.pdf 

The manipulated portions of the signature appearance were contained in 
layers n1, n3 and n4. Beginning with version 6, Acrobat does not 
maintain support for signature appearances that can be manipulated, 
though legacy signatures with these appearances may continue to display 
correctly. Use of layers n1, n3, and n4 is not recommended.
The standard XObject layers are as follows:
n0 — Background layer, as preset when creating the signature field, for 
example by using the Acrobat
form creation tool. In the example appearances in Example signatures on 
page 7, this layer is blank.
n2 — Signature appearance layer, containing information about the 
signature. In the example Unverified signature, this is the layer that 
contains the line art for the handwritten signature and the text giving 
the name, date, reason and location of the signature. The content of 
this layer can be dynamically created when the signature is created, but 
thereafter remains static. Specifically, it remains static when the 
validity state is changed.