Fonts are being mangled by the PDF Editor
To Reproduce (current behavior)
- Open a PDF with embedded fonts that are not resident in the operating system. A bit of sheet music is a good example.
- Select a bit of text and then click on Edit Text on the context menu that pops up
- Observe that embedded but non-resident font glyphs are now mangled
Desired Behavior:
Firstly, do not substitute any fonts simply because the user went into Edit mode. In my case, I just wanted to remove some underlining and remove a line shape.
If the user types a character that is not encoded in the embedded font, do the folowing:
- search for nearest-match fonts by using the embedded font glyphs to look for fonts on the system or online that match the encoded glyph vectors, bounding boxes, bitmap representation. This should produce a list of nearest match candidates.
- If an exact match is found online, offer to download it and use it in the application (embedding more glyphs or whole font into the document)
- If no exact match is found, display a dialog box to the user, showing the top-n best matching fonts (with examples of how characters will look in that font using the current font styles) and let the user choose the font to use to add additional letters to the document.
- Of course, the user should have the option to add nothing, in which case, the system ignores the typed letter that caused the substitution attempt
- User should be given the option, when selecting the font, to perform a global document-wide substitution of the new font for the incomplete embedded one. If they choose not to, only letters they type that are not in the active embedded font are added
This will preserve the existing appearance of the document with maximum fidelity, while giving the user reasonable options to address the incompleteness of the existing embedded font.