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How to repair a pdf that can't be merged
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Posted by pks  · 25-08-2021 - 20:21

I'm trying to merge multiple PDFs with MultiMerge mergePdf() function, which works most of the time. In a specific case/file, the process fails with this error:

Fatal error: Uncaught exception 'Exception' with message 'TCPDF_PARSER ERROR: decodeFilterFlateDecode: invalid code' 

I've followed the tutorial here:
and in case the merging process fails, I automatically repair all pdfs with pdftocairo then I try to merge again. WIth the repaired PDFs now I get to a different error, an infinite loop crash:

Furthermore, I discovered that even with good files that can be merged by phpdocx, if I go through the pdftocairo repair process before, I get to the exact same infinite loop that ends with an out of memory error.

Is this a corrupted file issue, pdftocairo messes up the files worse than they are? Both the original and the repaired pdfs open fine in readers, browsers, etc. Has anyone experienced anything similar? I can provide the file in case on private if needed.

Posted by admin  · 26-08-2021 - 05:37


Please try using the following command to repair the PDF that uses ghostscript instead of pdftocairo:

gs -o document_repaired.pdf -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress document.pdf

If you send the PDF document to contact[at] we'll check it.


Posted by pks  · 26-08-2021 - 08:25

Thank you for the quick reply and suggestion - it worked! If it's not too much trouble, I would advise completing this article:

with the Ghostscript idea and command line, it could save hours of debugging for other users.

Posted by admin  · 26-08-2021 - 08:42


The page has been updated in the current testing branch of the website, it will be updated in the coming days.