As of October 1997, papers published before 1996 are no longer listed. Papers are welcome in any of five formats. Any modern word-processor can produce PostScript output. It is a good idea to print the PostScript file on someone else's printer to be sure that it will work, before submitting it to the archive. Documents are searchable.
Any printer can print it.
Anybody can view it on screen. Document is searchable. Abstract only, with link to full paper at the author's own site. The author can easily put an updated version of the paper in place. Abstract only, author mails hard copy.