[Poppler-bugs] [Bug 50750] pdftops generates broken (according to ghostscript) postscript

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=50750

--- Comment #3 from Stefan Brüns <stefan.bruens at rwth-aachen.de> ---
Reading a bit more, I can state the following:

The PDF file is obviously broken. The /Differences array in the /Encoding dict
contains invalid/broken entries:
- The names are invalid (invalid characters)
- Different code points have the same name

While the latter is not invalid (e.g. .notdef is commonly used for all
codepoints without glyphs), it is obviously broken, as the codepoints refer to
*different* glyphs.

There are two possible solutions I can see here:

1. The file is broken. Call it a day

2. Follow the standard PDF32008-1:2008, 9.6.6.4 [1]:
---
 If a (3, 1) “cmap” subtable (Microsoft Unicode) is present:
 • A character code shall be first mapped to a glyph name using the table
described above. 
 • The  glyph  name  shall  then  be  mapped  to  a  Unicode  value  by
consulting  the  Adobe  Glyph  List (see  the Bibliography). 
 • Finally, the Unicode value shall be mapped to a glyph description according
to the (3, 1) subtable.

[...]
In any of these cases, if the glyph name cannot be mapped as specified, the
glyph name shall be looked up in the font program’s “post” table (if one is
present) and the associated glyph description shall be used. 
[...]
If a character cannot be mapped in any of the ways described previously, a
conforming reader may supply a mapping of its choosing. 
---
This will fail in the first step; it has no 'post' table, thus the third
paragraph applies.

As we know names in the AGL are ascii only, we can reject the bad names from
the differences array, and in this case end up with the names from
WinAnsiEncoding. 


[1] https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf
[2] Adobe Glyph List (AGL):
https://github.com/adobe-type-tools/agl-aglfn/blob/master/aglfn.txt

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