Fill and sign for PDF file not working using Acrobat Reader DC

[Dave Nottage 490]

Kind of off-topic, however the PDF being generated is from Delphi code. I have a question on SO about it:

 

https://stackoverflow.com/questions/62443834/fill-and-sign-for-pdf-file-not-working-using-acrobat-reader-dc

 

Any insights into what the problem may be would be appreciated

[Guest]

I don't have Adobe Acrobat, just hate it !

 

Anyway, my two cents about that interesting behaviour

1) I compared these files in text format and there is two extra objects ( not really extra but different and looks they been injected later stage) in the one named SigningNoWork

2) The object 15 in that file is interesting as it is encoded stream while it is very short (60 bytes) and such size doesn't really need compression, (basic sense)

3) To confirm my suspicion that you used two different software (or libraries) to generate these files, and one went ahead and added secret (invisible/ hidden watermark)

4) Googled online service to decompress pdf, found one and decompressed that file 

5) Now it may start to make sense as the encoded stream is in fact decompress to this

 

Quote

15 0 obj
<<
/Filter /FlateDecode
/Length 60
>>
stream
             ////////////////// not pasted
endstream
endobj

//////////////////////// after decompression 

15 0 obj 
<<
/CreationDate (D:20200618155607)
/Producer (WSYS Custom PDF)
/Author (WSYS)
/Title (PDF DOCUMENT)
>>
endobj

The same file does has this meta data

Quote

<pdf:Producer>Wave Systems PDF</pdf:Producer>
<xmp:CreateDate>2020-06-16T10:42:21Z</xmp:CreateDate>
<xmp:CreatorTool>Wave Systems PDF</xmp:CreatorTool>
<xmp:MetadataDate>2020-06-16T01:19:54Z</xmp:MetadataDate>
<xmp:ModifyDate>2020-06-16T01:19:54Z</xmp:ModifyDate>

So creation date in that encoded stream points to changes in the file and hidden information, or just wrongly adding such date !, in any case it did hide it !, this may be the reason that Acrobat Reader refused to sign it.

 

Dave, i don't think you can find 100% accurate answer to the reason in the question, as pdf format is somewhat unrestrictive, allowing such behaviour, but on other hand i trust Acrobat reader for its security (to name it right, lack of it and updating/patching, it almost on weekly basis)

My suggestion is keep away from any library or software that adds hidden meta data, if you can't then directly ask the author to provide you with clean library. 

 

Hope this help, and didn't waste your time.

[Dave Nottage 490]

1 hour ago, Kas Ob. said:

Hope this help, and didn't waste your time.

All good, thanks. Someone has answered who spotted a discrepancy that I missed, namely in the font widths array. What's worse: I missed that the "one that works" had altered the font info to correct the problem.