Keep tiny characters.
void pdfSetTextKeepTinyChars(int keep)
By default, XpdfText will discard tiny (smaller than 3 point) characters after the first 50,000 per page. This avoids problems with slow run times due to PDF files that use special fonts to do shading or cross-hatching. Calling this function with a non-zero argument disables this behavior and tells XpdfText to keep all characters.

This setting is global - it applies to all PDF handles.