Re: Unicode Support in Adobe Acrobat

From: Eric Muller (
Date: Mon May 02 2005 - 16:40:07 CDT

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    Rick Cameron wrote:

    >Thanks for the explanation. As you say, it's unfortunate that the PDF
    >spec uses misleading terminology for these concepts.
    There is a good excuse: a fair amount of the PDF terminology comes from
    the PostScript world, which originated before 1985. While work on
    Unicode and the character/glyph model was certainly underway, it was
    also far from being the lingua franca.

    >I seem to recall that the fonts used in a PDF file are restricted in the
    >number of glyphs they can have. IIRC the limit is 256. Thus, when our
    >app produces PDF files it has to split a large font into several derived
    >fonts, and make mappings from Unicode code points to glyph indices in
    >these derived fonts.
    Short answer: it is possible to have fonts with large glyph complements
    in PDF.

    Long answer: PDF provides multiple (too many?) mechanisms, known as font
    encodings, to go from the "character codes" to actual glyphs in fonts.
    Some of those (simple fonts, PDF spec section 5.5) are applicable only
    when the possible range of character codes is limited to [0 ... 255].
    Others (composite fonts, PDF spec section 5.6) are applicable to
    character codes in the range [0 ... 0xffff].

    >It would be far more convenient if it were possible to use Unicode code
    >points as glyph indices.
    >Has this situation changed?
    Philippe expressed consisely what I was trying to say: "the PDF document
    is a *rendered* document, so it needs to reference glyphs rather than
    abstract characters." That's the nature of the beast.

    If you have *character strings* in your hands and you want to generate a
    PDF that renders those strings, you need a layout engine.

    >If not, is it likely to change in the
    Regardless of what I know or don't know about future products, I cannot


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