Created attachment 138181 [details]
I received a file from gour on the poppler IRC. With recent versions of cairo, printing with evince adds some characters to the document. I don't believe I'm allowed to share the original file so I'm attaching this anonymized version.
This is reproducible through poppler's pdftocairo program. Running `pdftocairo -pdf anonymized.pdf bad.pdf` produces a pdf that shows additional characters. I traced the regression to this commit:
commit 495362279b42620071c6b46f69918ce324aee0db (refs/bisect/bad)
Author: Adrian Johnson <firstname.lastname@example.org>
Date: Sun Sep 27 08:27:53 2015 +0930
scaled-font-subsets: if glyph 0 used for rendering, remap to different index
Some broken pdfs use glyph 0 in embedded fonts for rendering instead of .notdef.
The cmap we use for embedding latin fonts does not allow rendering glyph 0. Ensure
if glyph 0 is used, it is mapped to a non 0 glyph in the subset.
This PDF includes a character mapped to glyph index 0. It's not supposed to be visible in the document, but after `pdftocairo -pdf` conversion it is.
Created attachment 138182 [details]
rendering of anonymized.pdf is good
Produced by `pdftocairo -png -singlefile anonymized.pdf good`. Rendering of anonymized.pdf, before processing by `pdftocairo -pdf`, is correct.
Created attachment 138183 [details]
processed pdf from `pdftocairo -pdf`
PDF created by `pdftocairo -pdf anonymized.pdf processed.pdf`. The conversion process adds a character to the document.
Created attachment 138184 [details]
rendering or processed.pdf is bad
Produced by `pdftocairo -png -singlefile processed.pdf bad`. Rendering of processed.pdf shows a new character in the image.
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