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?
There are many good reasons why PDF has a “render glyph” instruction instead of a “render string”. In particular your printer and your PDF viewer should not need to have the same text shaping and layout algorithms in order for the PDF to render the same. Oops, your printer runs a different version of Harfbuzz!
The sibling comment is right that a lot depends on the software that produced the PDF. It’s important to be accurate about where the blame lies. I don’t blame the x86 ISA or the C++ standards committee when an Electron app uses too much memory.