| apib | API Blueprint Document |
| apo | Abacre Paperless Office Portable Document |
| apr | Lotus Approach 97 Document |
| apxl | iWork Keynote XML Presentation |
| ard | Alphacam Router Drawing |
| ark | OpenBook Document |
| arr | Remedy ARS Report |
| art | ArtCAM Model File |
| art3 | Art Text Drawing |
| art6 | Articulate Presenter Online Document |
| article | Twixl Publisher Article |
| as5 | CivilCAD v5 ASCII Document |
| asc | ASCII Armored GPG/PGP File |
| asc | Plain Text Document |
| ascii | Plain Text Document |
| asd | Alphacam Stone Drawing |
| asd | Microsoft Word AutoRecovery File |
| ase | Autodesk 3D Studio ASCII Scene Export |
| aseprite | Aseprite Sprite Data |
| asm | Solid Edge Assemblies Document |
| assbin | Allegorithmic Substance Painter Scene |
| ast | ClarisWorks Assistant |
| astx | Adobe Story Exported Script |
| asy | Asymptote Document |
| at2 | Aldus Persuasion v2 Template |
| at65 | Adobe PageMaker for Mac 6.5 Template |
| atd | Alphacam Lathe Drawing |
| atom | Atom Syndication Format File |
| atw | AnyTime Organizer Deluxe Document |
| aty | Association Type Placeholder |
