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Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Fri, 24 Oct 2014 04:00:39 GMT

Hi, I'm just wondering what happens in the below situation.

We have a Page which includes a form XObject #1, which itself contains another form XObject #2.
Form #2 uses a font but has no Resources dictionary. The font is defined against the Resources dictionary of form #1 instead.

Based on the PDF spec (which I've copied below) a client application should refer to the original Page object to see if the font is defined there but should not check form #1. We should therefore get a missing font error as the PDF is invalid. Is this correct?

For reference the PDF spec v1.4 says the below.

"A form XObject or a Type 3 font’s glyph description may omit the Resources entry, in which case resources will be looked up in the Resources entry of the page on which the form or font is used. This practice is not recommended."

Is a zero length glyf table valid for a TTF subset?

forums_noreply@adobe.com — Fri, 24 Oct 2014 06:02:10 GMT

I've posted related queries in a few forums - there is some background info at https://forums.adobe.com/thread/1611899 and it was suggested I ask the experts here

Basically in some situations InDesign is generating a subset font with a zero length glyf table.

Does this 'exists but zero length' table fulfil the criteria from the PDF specification?

The following TrueType tables are always required: “head,” “hhea,” “loca,” “maxp,” “cvt_,” “prep,” “glyf,” “hmtx,” and “fpgm.”

A number of programs are not happy with such files, but Adobe products seem to handle them. However Acrobat in particular is fairly forgiving as we all know.

Microsoft's font validator says the subset is not valid. Programs like Ghostscript attempt to fix it by adding an empty table.

Subset font missing glyf table

forums_noreply@adobe.com — Sun, 19 Oct 2014 23:35:45 GMT

When saving a PDF with InDesign if there is a TrueType font where the only used character is a space, the resulting embedded TrueType subset is missing the 'glyf' table. Acrobat seems OK with this but it causes problems with other tools.

For example, Ghostscript cannot re-encode the font since important information is missing. At least one of our printers fails to print the file. As I understand it every font needs a 'glyf' table for at least the .notdef glyph and maybe more.

This is an odd case with an easy workaround but as we have clients giving us files from external agencies it incurs a lot of delay because we usually won't realise the problem until printing fails, and we have to go back to the source to get it fixed.

Is this a bug, or considered valid? Acrobat not complaining is not really any indicator since it accepts many broken files. I've checked this with CS6 and CC 2014.

Can preflight detect missing glyphs?

forums_noreply@adobe.com — Thu, 23 Oct 2014 04:20:19 GMT

We have an issue where InDesign is writing out subset TrueType fonts with a zero-length 'glyf' table. We want to detect this in preflight as the file will not print because the font is invalid.

I have posted some details at Re: Subset font missing glyf table relating to the InDesign problem.

So far I have tried the following preflight checks but none of them fire: "Character reverts to .notdef", "Embedded font contains all glyphs needed in PDF", "Font is not valid", "Font subset contains all glyphs used in page description".

This is in Acrobat 9. I have also browsed the internal font structure. Acrobat seems OK with the fact the glyf table is zero length. It actually says there are 234 glyphs in this empty table, but they just happen to also be zero length (listed under 'Glyphs Without Data'). I believe this is due to the loca table, which again has 234 entries, all of zero length and offset (listed under 'Locations Without Data').

So it basically says all the characters exist so there's no problem. I don't really agree with that.

Is there a way to detect this problem in Acrobat preflight? I can detect this with a custom script but I'd rather keep our workflow simple