zlacker

>>heyden+(OP)
> This remains a long-standing pet peeve of mine. PDFs like this are horrible to read on mobile phones, hard to copy-and-paste from ...

I've never understood why copying text from digitally native PDFs (created directly from digital source files, rather than by OCR-ing scanned images) is so often such a poor experience. Even PDFs produced from LaTex often contain undesirable ligatures in the copied text like fi and fl. Text copied from some Springer journals sometimes lacks space between words or introduces unwanted space between letters in a word ... Is it due to something inherent in PDF technology?

>>aragon+Nda
ligatures like fi fl ffi ffl etc are for changes in fonts specific to rendering correctly on a screen or printer. It's intended to be a _rendered_ format, rather than a parse-able format.

Well formatted epub and HTML generally are usually intended to update to end user needs and better fit available layout space.

>>mjevan+aea
Though it's also a stuck legacy throwback. Modern advice would be to not send ligatures directly to the renderer and instead let the renderer poll OpenType features (and Unicode/ICU algorithms) to build them itself. PDF's baking of some ligatures in its files seems something of a backwards compatibility legacy mistake to still support ancient "dumb" PostScript fonts and pre-Unicode font encodings (or least pre-Unicode Normalization Forms). It's also a bit of the fact that PDF has always been confused about if it is the final renderer in a stack or not.

>>WorldM+Ulb
That wouldn’t work for PDF’s use case of being an arbitrary paper-like format because the various Unicode and OpenType algorithms don’t provide sufficient functionality for rendering arbitrary text: there are no one-size-fits all rules! The standards are a set of generic “best effort” guidelines for lowest-common-denominator text layout that are constantly being extended.

Even for English the exact tweaking of line breaking and hyphenation is a problem that requires manual intervention from time to time. In mathematics research papers it’s not uncommon to see symbols that haven’t yet made it into Unicode. Look at the state of text on the web and you’ll encounter all these problems; even Google Docs gave in and now renders to a canvas.

PDF’s Unicode handling is indeed a big mess but it does have the ability to associate any glyph with an arbitrary Unicode string, for text extraction purposes, so there’s nothing to stop the program that generates the PDF from mapping the fi ligature glyph to the to-character string “fi”.