text becomes invisible when combining in acrobat

So...strange situation that I can't figure out why it's happening. A user came to me and said when they combine .pdf document 1 with .pdf document 2, some of the text from document 1 disappears. Not all, just text in a few headers. Document 1 is a .pdf that was created inside an app (prolog manager). Document 2 was created by a customer (and I believe was created by combining Word documents and scanned documents). First thing I discovered is that the text didn't disappear, it just becomes invisible or transparent. I can actually copy it out and paste it into a text file and see the text. Secondly, I discovered by trial and error is that, if I leave out one of the pages in document 2 and then combine with document 1, all the text stays visible, no issues, but if I throw that one page back in, the text then disappears from document 1. Thirdly I discovered, is that if I cut out the problem child page from document 2 and paste into Word, then save it and make it a .pdf and then combine back into the original document 2 and then combine with document 1, the text stays visible, no issues. So what I think I determined is that this one page from document 2 was possibly created in a way that is causing havoc. So, now my question.....why? I saw this one other time, but I don't have details other than, there was a bad page or two and when removed, the file was fine; I was hoping it was just a fluke, but now it's showing up again. Any help is appreciated!! Joneo99


Sordoni IT


2 Answers

Voted Best Answer

The problem is related to fonts. You can have fonts used in a PDF file in three different ways:

  • The font is not embedded, so whenever the PDF is being displayed or printed, it will reference the font on the local computer. This is not a problem with fonts that are available on all computers, but when you use a font that exists for example only on Windows computers, and then you display this PDF file on a Mac, you will have a problem.
  • A font can be fully embedded in the PDF file. In this case, there is no question about what to use when viewing or printing the PDF file, the font travels with the document. This is a problem if you have very large fonts (e.g. Asian fonts are huge and would expand the file size considerably), but it's also a problem if you are only using a handful of characters of a font (e.g. for a title).
  • A font can be subset embedded in the PDF file. In this case, you are only embedding those characters that are actually used in a document. If you write a book that's called "SOS", and you use a special font for the book title, you can get away by just embedding the "glyphs" (that's the drawings of the characters) for "S" and "O", and that would make your file much smaller.

Now that we know how fonts can be used in a PDF file, let's take a look at what is happening with your files when you combine them. This is just based on what I've experienced in the past, I don't have access to your documents, so I have to make certain assumptions, and I may be wrong, but based on the symptoms, I think I have a pretty good understanding of what's going on:

Both of your documents use the same font, but with different subsets. This is usually not a problem, Adobe created some rules about how to name subsets to that Acrobat "knows" that two subsets are actually different (e.g. one contains the glyphs for "ABCDEFghijklm012345", and the other one the glyphs for "ABCXYZabcmnop567". You can see that we have some overlap, but there are glyphs that are only in the first subset, and there are glyphs that are only in the second subset.

If one of your documents (and by experimenting with the documents, you've narrowed it down not just to the document, but the actual page) has a subset that is not correctly marked, Acrobat may assume that both subsets are identical, and it does not merge the two subsets and therefore does not embed the gyphs for some of the subsets. This results in characters disappearing from your other PDF document because those glyphs are not used in the second document.

You found a workaround that fixes this problem in your case, there is unfortunately no generic fix for these problems.

Would you be able to share the documents with me? I'd like to take a look to see if there is something you could do within Acrobat to fix the problem.

Hope this helps.

Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com


By Karl Heinz Kremer   

It's been a while, but if you run into this problem again, here is a potential workaround:

http://khkonsulting.com/2015/02/missing-characters-merging-inserting-pdf-files-potential-workaround/


Karl Heinz Kremer   


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