It is a well known critique against (PDF)LaTeX in the german speaking region that LaTeX tend to mess up umlaute (äöü) by composing them by the base letter (aou) followed by a diacritic character. The causes for this are buried deep somewhere in the inner guts of LaTeX/TeX (at least for me as a dumb user). However, this can be avoided by using "T1" fonts. Therefore not a general problem and i kept promoting the usage of LaTeX for scientific writing (Theses, Papers etc.) as the way to go to my colleagues.
Then i was struck when i experienced that copying and pasting text with diacritics (in fact umlaute in a german title of a reference) from my thesis pdf, opened in preview on my mac, in my text editor (sublime edit) produced this: