EpubCCWhat is a ToUnicode map?
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A ToUnicode map (CMap) is a table in a PDF font that says which Unicode character each glyph represents. Without it, a program can draw the text but may not know what the letters are.
Why it matters when you convert a PDF to EPUB
When the map is missing or wrong, the PDF looks fine but its extracted text is gibberish, symbols or empty: copying and pasting from it shows the same problem. A converter cannot recover the right characters from such a font without OCR, so the EPUB inherits the problem.
How EpubCC handles it: the engine does not guess letters for glyphs that have no Unicode value. When a page has many of them, the quality report warns about glyphs without Unicode, so you know from the free sample which pages will need OCR or a better source file before you pay for the whole book.
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