| Index Format | |
| N/A | |
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File with an .IDX extension contains an index of files or data within a given space, for instance a disc or a catalogue. Indexing allows more efficient algorithm searching or sorting, thanks to which, user can obtain the results faster.
IDX files are used by different types of software, for instance Corel QuickFinder, ESRI ArcView, Microsoft FoxPro, ICQ, and also for purpose of databases indexing.
Windows
Mac OS
| .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 |