PDF Certification invalid : "Document has been altered or corrupted since it was signed"

Question

I am doing a PDF signing feature for my application. Here is the workflow :

1. The PDF is stored on the server.
2. I include all the signatures fields necessary into the file and compute the byterange etc using an extension of ZendPDF called FaritPDF.
3. I compute the hash according to the computed ByteRange using SHA256.
4. The hash is sent to the client.
5. The client sign the hash using a PFX file and creates a PKCS7 object containing the hash.
6. The PKCS7 object is sent to the server.
7. The PKCS7 object is included in the PDF and the PDF is rendered.

Which leads me to the following error : "Document has been altered or corrupted since it was signed". The ByteRange is correct, I didn't modify any byte of the file. I am using the same algorithm as Acrobat Reader. What could I be doing wrong ?

Here is my PDF file, sorry I can't upload it from work :

%PDF-1.3
%âãÏÓ

1 0 obj
<<
/Type /Catalog
/Outlines 2 0 R
/Pages 3 0 R
>>
endobj

2 0 obj
<<
/Type /Outlines
/Count 0
>>
endobj

3 0 obj
<<
/Type /Pages
/Count 2
/Kids [ 4 0 R 6 0 R ] 
>>
endobj

4 0 obj
<<
/Type /Page
/Parent 3 0 R
/Resources <<
/Font <<
/F1 9 0 R 
>>
/ProcSet 8 0 R
>>
/MediaBox [0 0 612.0000 792.0000]
/Contents 5 0 R
>>
endobj

5 0 obj
<< /Length 1074 >>
stream
2 J
BT
0 0 0 rg
/F1 0027 Tf
57.3750 722.2800 Td
( A Simple PDF File ) Tj
ET
BT
/F1 0010 Tf
69.2500 688.6080 Td
( This is a small demonstration .pdf file - ) Tj
ET
BT
/F1 0010 Tf
69.2500 664.7040 Td
( just for use in the Virtual Mechanics tutorials. More text. And more ) Tj
ET
BT
/F1 0010 Tf
69.2500 652.7520 Td
( text. And more text. And more text. And more text. ) Tj
ET
BT
/F1 0010 Tf
69.2500 628.8480 Td
( And more text. And more text. And more text. And more text. And more ) Tj
ET
BT
/F1 0010 Tf
69.2500 616.8960 Td
( text. And more text. Boring, zzzzz. And more text. And more text. And ) Tj
ET
BT
/F1 0010 Tf
69.2500 604.9440 Td
( more text. And more text. And more text. And more text. And more text. ) Tj
ET
BT
/F1 0010 Tf
69.2500 592.9920 Td
( And more text. And more text. ) Tj
ET
BT
/F1 0010 Tf
69.2500 569.0880 Td
( And more text. And more text. And more text. And more text. And more ) Tj
ET
BT
/F1 0010 Tf
69.2500 557.1360 Td
( text. And more text. And more text. Even more. Continued on page 2 ...) Tj
ET
endstream
endobj

6 0 obj
<<
/Type /Page
/Parent 3 0 R
/Resources <<
/Font <<
/F1 9 0 R 
>>
/ProcSet 8 0 R
>>
/MediaBox [0 0 612.0000 792.0000]
/Contents 7 0 R
>>
endobj

7 0 obj
<< /Length 676 >>
stream
2 J
BT
0 0 0 rg
/F1 0027 Tf
57.3750 722.2800 Td
( Simple PDF File 2 ) Tj
ET
BT
/F1 0010 Tf
69.2500 688.6080 Td
( ...continued from page 1. Yet more text. And more text. And more text. ) Tj
ET
BT
/F1 0010 Tf
69.2500 676.6560 Td
( And more text. And more text. And more text. And more text. And more ) Tj
ET
BT
/F1 0010 Tf
69.2500 664.7040 Td
( text. Oh, how boring typing this stuff. But not as boring as watching ) Tj
ET
BT
/F1 0010 Tf
69.2500 652.7520 Td
( paint dry. And more text. And more text. And more text. And more text. ) Tj
ET
BT
/F1 0010 Tf
69.2500 640.8000 Td
( Boring.  More, a little more text. The end, and just as well. ) Tj
ET
endstream
endobj

8 0 obj
[/PDF /Text]
endobj

9 0 obj
<<
/Type /Font
/Subtype /Type1
/Name /F1
/BaseFont /Helvetica
/Encoding /WinAnsiEncoding
>>
endobj

10 0 obj
<<
/Creator (Rave \(http://www.nevrona.com/rave\))
/Producer (Nevrona Designs)
/CreationDate (D:20060301072826)
>>
endobj

xref
0 11
0000000000 65535 f
0000000019 00000 n
0000000093 00000 n
0000000147 00000 n
0000000222 00000 n
0000000390 00000 n
0000001522 00000 n
0000001690 00000 n
0000002423 00000 n
0000002456 00000 n
0000002574 00000 n

trailer
<<
/Size 11
/Root 1 0 R
/Info 10 0 R
>>

startxref
2714
%%EOF
1 0 obj 
<</Type /Catalog /Outlines 2 0 R /Pages 3 0 R /Perms <</DocMDP 11 0 R >> /AcroForm <</Fields [12 0 R ] /SigFlags 3 >> /Names 15 0 R >>
endobj
3 0 obj 
<</Type /Pages /Count 2 /Kids [4 0 R 6 0 R ] >>
endobj
4 0 obj 
<</Type /Page /Parent 3 0 R /Resources <</Font <</F1 9 0 R >> /ProcSet 8 0 R >> /MediaBox [0 0 612 792 ] /Contents 5 0 R >>
endobj
6 0 obj 
<</Type /Page /Parent 3 0 R /Resources <</Font <</F1 9 0 R >> /ProcSet 8 0 R >> /MediaBox [0 0 612 792 ] /Contents 7 0 R >>
endobj
11 0 obj 
<</Type /Sig /Filter /Adobe.PPKLite /SubFilter /adbe.pkcs7.detached /ByteRange [0 3660 15404 678                   ] /Contents <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> 
/Reference [<</Type /SigRef /TransformMethod /DocMDP /TransformParams <</Type /TransformParams /V /1.2 /P 3 >> >> ] /M (D:20170720170036+02'00') >>
endobj
12 0 obj 
<</Type /Annot /SubType /Widget /Rect [0 0 0 0 ] /P 4 0 R /F 4 /FT /Sig /T (Signature) /Ff 0 /V 11 0 R >>
endobj
13 0 obj 
[]
endobj
14 0 obj 
<</Names 13 0 R >>
endobj
15 0 obj 
<</Dests 14 0 R >>
endobj
xref
0 2 
0000000000 65535 f 
0000003028 00000 n 
3 2 
0000003179 00000 n 
0000003243 00000 n 
6 1 
0000003383 00000 n 
11 5 
0000003523 00000 n 
0000015561 00000 n 
0000015684 00000 n 
0000015704 00000 n 
0000015740 00000 n 
trailer
<</Size 16 /Root 1 0 R /Info 10 0 R /Prev 2714 >>
startxref
15776
%%EOF

Answer 1

Your assertion that you did not modify any byte of the file is contradicted by step 7. You may want to diff the before and after of step 7 and make sure that the PKCS7 object is being written in the part of the file that is not part of the byterange used to calculate the hash.