PDF is a render-only format with optional hidden metadata for semantics. The PDF file they created knows how to paint the ligatures they used, like "fi" and "f

PDF is a render-only format with optional hidden metadata for semantics. The PDF file they created knows how to paint the ligatures they used, like "fi" and "ff", but doesn't contain the `/ToUnicode` metadata for what those symbols meant. The generated PDF happened to put the "fi" ligature at an index that is normally used "Ö", and didn't provide more information.