Many people know what I'll say here, but I thought the re-format of the situation was appropriate...
For mathematics and "hard" sciences, PDF (portable document format) is absolutely standard now. Until a few years ago, PS (postscript) and DVI (device independent) formats were typical, but no more.
In mathematics, "Word" format was never common.
Currently, traditional (meaning various things) mathematics journals want a PDF file to send to referees. Everyone has software that can convert PostScript files to PDF, and so on. In fact, "OpenOffice", for example, can convert/export "Word" files to PDF.
So, in sciences, PDF, though "Word" may be forgivable.
The question of future readability of these or any other file formats is hugely non-trivial. (Similarly, kids-these-days, such as my almost-20 daughter, have great difficulty reading "cursive writing" of "old" people. :)
So: modulo issues that the original questioner can't afford to worry about, the current answer is "PDF, and tolerance for Word files, esp. from the humanities...".
The long-term answer about survivable file-formats... is troubling. :)