Errors detected in the XREF table

PDF-XChange Editor SDK for Developers

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AnMuWK
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Posts: 20
Joined: Thu Dec 19, 2019 2:20 pm

Errors detected in the XREF table

Post by AnMuWK » Tue Mar 10, 2020 11:02 am

Hi,

I am experiencing an issue with the PDF-XChange Editor, which is integrated into our product.

Our product is producing pdf documents (using MS Word) which are then digitally signed using a 3rd-party API.
When viewing these signed PDF's, the editor always shows a red toolbar at the top, where a button opens a window with an error message, saying 'Errors detected in the XREF table' (translated from german) - Please see the attached screenshot.

I checked with our 3rd-party API's vendor, and they could not find anything wrong with our pdf files.
I also checked the validity of said pdf files using

- JHOVE (https://github.com/openpreserve/jhove)
- cpdf (https://community.coherentpdf.com)
- pdfinfo from XPdf (http://www.xpdfreader.com/pdfinfo-man.html)

but none of these reported any problems with the pdf files, neither does the latest version of Adobe Reader.

The error is only shown for signed pdf's, unsigned pdf's are perfectly fine.
I also tried signing pdf files with different pdf conformity levels (A-1a, A-2a, etc.) but this doesn't seem to have any effect, the error still persists.

The most likely conclusion seems to be that this error message is a false-positive that is specific to the PDF-XChange Editor.
Thus, I would like to ask of you the following:

1) Could you please check why this message is displayed in the PDF-XChange Editor? Attached you can find two pdf files, one is the original pdf document (without signature) and the other is the signed document, producing the mentioned error message.

2) Is it possible to hide the error toolbar when embedding the PDF-XChange Editor in our product? Even if a pdf file is malformed, we don't want this error-toolbar to be shown - rather would we display this information ourselves, if at all.

Best regards,
Andreas
Attachments
TestDocument_signed.pdf
Signed PDF File
(47.45 KiB) Downloaded 22 times
TestDocument.pdf
Original (unsigned) PDF File
(37.21 KiB) Downloaded 19 times
Tracker_Error_1.png
Screenshot Error Message

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Sasha - Tracker Dev Team
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Re: Errors detected in the XREF table

Post by Sasha - Tracker Dev Team » Tue Mar 10, 2020 1:39 pm

Hello Andreas,

As for the first question, you can ask it in the End-User Editor forums - you should be assisted there.
As for the second question - the IPXV_Document::InfoBar property allows you to obtain the IPXV_DocInfoBar interface. From there, you can modify it to your liking and also hide/show it.

Cheers,
Alex
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Lzcat - Tracker Supp
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Re: Errors detected in the XREF table

Post by Lzcat - Tracker Supp » Tue Mar 10, 2020 4:17 pm

Hi Andreas.
Problem is in tool used to sign PDF, it create not fully correct PDF file.
Here is part of signed PDF file where error is:

Code: Select all

xref
0 1 
0000000000 65535 f
30 1 
0000038109 00000 n
3 1 
0000038142 00000 n
22 1 
0000038338 00000 n
23 1 
0000038373 00000 n
24 1 
0000038473 00000 n
25 1 
0000038589 00000 n
21 1 
0000039962 00000 n
7 1 
0000040146 00000 n
1 1 
0000040417 00000 n
26 4 
0000040785 00000 n
0000040965 00000 n
0000044543 00000 n
0000044725 00000 n
trailer
<<
/Size 32
/ID [<970B0C4F1088044CA4DAF79C123FFC7F><E71F482347E715FB9DB35235E8D22649>]
/Info 7 0 R
/Root 1 0 R
/Prev 37533
>>
startxref
As you can see in trailer dictionary stated that PDF file will contain 32 objects (including free object with number 0), so maximum object number in PDF should be 31. But in xref table and file itself maximum object number is 30, which does not match information in trailer. This is why Editor display notification.
Also, there is three other minor disadvantages in xref table itself:
1. Object with number 0 listed second time (not needed, add 26 extra bytes to file)
2. Updated object listed in xref in arbitrary order (not critical, but may affect some programs; most pdf modification software write them in order of increasing object numbers).
3. Objects 21-30 are listed in six different sections instead of one, which also waste file size (35 additional bytes in current file) and also may slightly affect speed of pdf processing.
HTH.
Victor
Tracker Software
Project manager

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AnMuWK
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Posts: 20
Joined: Thu Dec 19, 2019 2:20 pm

Re: Errors detected in the XREF table

Post by AnMuWK » Wed Mar 11, 2020 8:33 am

Thank you for your detailed explanation!
I'll relay it to our 3rd-party vendor, hopefully the will be able to fix it.

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Will - Tracker Supp
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Re: Errors detected in the XREF table

Post by Will - Tracker Supp » Wed Mar 11, 2020 9:22 am

:D
If posting files to this forum, you must archive the files to a ZIP, RAR or 7z file or they will not be uploaded.
Thank you.

Best regards

Will Travaglini
Tracker Support (Europe)
Tracker Software Products Ltd.
http://www.tracker-software.com

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