| Microsoft Help 2 Keyword Index Format | |
| Microsoft | |
| Ads |
Windows
| .aawdef | Ad-Aware Definitions Format |
| .abr | Adobe Photoshop Brush Format |
| .ac$ | AutoCAD Undo Info Format |
| .acc | DR DOS - ViewMax Format |
| .acl | Microsoft Office Automatic Correction List |
| .acs | Microsoft Agent Character Structured Storage Format |
| .ad | After Dark Screen Saver Format |
| .add | Microsoft Dynamics AX Developer Documentation Format |