[xep-support] PDF Accessibility?

[Nikolai Grigoriev]

Ryan,

> I am having problems making PDFs generated from XEP (3.6)
> accessible.  I get the following error when trying to add tags
> to the document in Acrobat 6:
> "Bad PDF; could not read page structure. <Bad PDF; error
> in processing fonts: cannot find CMap resource file>[1]"

I believe the problem stays within Acrobat Make Accessible plug-in.
The documentation for Acrobat 5.0 says:

> - Font Encodings: The MakeAccessible Plug-In maps fonts 
> used in the document to a Unicode value. In some cases, 
> a font encoding used within a PDF document does not 
> contain enough information for the MakeAccessible 
> Plug-In to map to a Unicode equivalent.

It looks like nothing changed in Acrobat 6.0.

Apparently, MakeAccessible is confused by /Identity-H
CMap that we use to specify encoding for TrueType fonts.
I wonder why it does so: there is an explicit /ToUnicode
CMap at each font descriptor. (You can test yourself
that TrueType text in our PDF files can be searched
and copied to the clipboard; this proves that the Unicode
mapping information is already there).

If I am right in my conclusions, the issue appears to be 
a real serious limitation of the plug-in. Have you spoken 
to Adobe about it?

Right now, I see no alternative to using /Identity-H 
for TrueType fonts. The only suggestion that comes 
to mind: switch to Type1 fonts. They don't use CMaps: 
perhaps things will be easier there. 

>  More generally, can anyone comment on XEP's support
> (or lack thereof) for creating accessible PDFs?

XEP 3.6 does not support tagged PDF out of the box.
We have plans in this direction, but it will inevitably
be a long run: tagging PDF is a tough task. (Adobe 
invented lots of tricky structures in the PDF, but 
didn't care even to define a standard character collection 
for plain Unicode. Sometimes, I have an impression 
that they deliberately complicate things for developers :-))

Regards,
Nikolai Grigoriev
RenderX 

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