.pdf is the most intelligent file format that I know, from my sad and bitter
experience. Standard text files are OK, .html is quite OK if you do not have
pictures, .docx is a moron and a source of curses from lovely, beautiful
colleagues who send you to the origins for not saving correctly, .doc is
something that we deal with every day, a well-known parasite and an excusable
stereotype. .odt is quite clearly as stupid as the former two but it is a good
altenative to M$ de facto monopoly. A necessary evil in the European jungle. I
warmly recommend .pdf or standard text.