[jl6]

This seems to be missing an important step in the use of qpdf’s --qdf mode: after you’ve finished editing, you need to run the file through the fix-pdf utility to recalculate all the object offsets and rebuild the cross-reference table that lives at the end of the file (unless you only change bytes in-place rather than adding or removing bytes).

My top 3 fun PDF facts:

1) Although PDF documents are typically 8-bit binary files, you can make one that is valid UTF-8 “plain text”, even including images, through the use of the ASCII85 filter.[0]

2) PDF allows an incredible variety of freaky features (3D objects, JavaScript, movies in an embedded flash object, invisible annotations…). PDF/A is a much saner, safer subset.

3) The PDF spec allows you to write widgets (e.g. form controls) using “rich text”, which is a subset of XHTML and CSS - but this feature is very sparsely supported outside the official Adobe Reader.

[0] For example: https://lab6.com/2

[gpvos]

After you've finished editing, just run it through qpdf without parameters, as explained in the beginning of the article, and it will recompress the data and recreate the xref table. No need for yet another tool.

[jl6]

I guess you could, but this is the source of the errors (actually warnings) that the article mentions. Probably best to fix the file with the provided tool (fix-qdf is distributed with qpdf) rather than get in the habit of ignoring warnings.

[gpvos]

OK. I have never needed or used fix-qdf and forgot about it, so your typo (fix-pdf) made me think it was from a different package.