For each PDF/A-1 validation issue we try to explain what it means and, if possible how to resolve it. For a more technical explanation of the issue we quote the related section of the ISO 19005-1 PDF/A Specification.
The document uses a subset of font characters but does not specify the subset in the font dictionary.
How can I fix it?
Use a PDF creation product that correctly encodes and embeds all fonts. We recommend Solid PDF Creator Plus.
6.3.5 - ISO 19005-1 PDF/A Specification:
As stated in 6.3.4, embedded font programs shall define all font glyphs referenced for rendering with a conforming file. Type 0 CIDFont and Type 1 and TrueType font subsets, as described in PDF Reference 5.5.3, may be used as long as the embedded font programs define all appropriate glyphs.
For all Type 1 font subsets referenced within a conforming file, the font descriptor dictionary shall include a CharSet string listing the character names defined in the font subset, as described in PDF Reference Table 5.18.
For all CIDFont subsets referenced within a conforming file, the font descriptor dictionary shall include a CIDSet stream identifying which CIDs are present in the embedded CIDFont file, as described in PDF Reference Table 5.20.
NOTE The use of font subsets allows a potentially substantial reduction in the size of conforming files.