| Abbreviation | Definition |
|---|---|
| APX | AppExpert database file |
| ARC | ARC or PKARC Compressed file archive |
| ARF | Automatic Response File |
| ARH | Archivers definitions file (DN) |
| ARI | ARI Compressed file archive |
| ARI | Aristotle Audio file |
| ARJ | ARJ Compressed file archive |
| ARK | ARC archive ( CP/M port of ARC file archiver) |
| ARK | ARC archive file |
| ARK | Managing your Money Archive file |
| ARK | QUARK Compressed file archive |
| ARR | Amber ARR image file Bitmap graphics |
| ARR | Atari Cubase Arrangement file |
| ART | First Publisher ART file Bitmap graphics (Black and White) |
| ART | Graphics (Another Ray Tracer - Vort) |
| ART | Vort Another Ray Tracer Graphics file |
| ARX | ARX Compressed file archive |
| AS | ActionScript |
| ASC | Armored encrypted file (Pretty Good Privacy) |
| ASC | ASCII text |