| 1 | Q | Cinematronics | Quantum Compressed File |
| 2 | Q7Q | N/A | India Ink Photoshop Plug-in |
| 3 | QAD | Corel Corporation | Corel WordPerfect Office Thumbnail |
| 4 | QB1 | Intuit Inc. | Quicken Data |
| 5 | QBD | Intuit Inc. | Quicken Keyboard Layout |
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| 6 | QBE | Corel Corporation | Corel Quattro Pro Saved Query |
| 7 | QBM | Intuit | QuickBooks Portable Company Format |
| 8 | QBO | Intuit | QuickBooks Online Bank Statement Format |
| 9 | QBQUERY | MySQL AB | MySQL Query Browser Saved SQL Query Command |
| 10 | QBX | Intuit | QuickBooks Accountant Transfer Format |
| 11 | QC | Valve | Half-Life Model Compiler Script |
| 12 | QCOW | David T Reynolds | QEMU Copy-On-Write |
| 13 | QCOW2 | David T Reynolds | QEMU Copy-On-Write |
| 14 | QDB | Intuit | Quicken 5 & 6 Data Format |
| 15 | QDF | Intuit | Quicken Data Format |
| 16 | QDFM | N/A | Quicken Data Format (Macintosh) |
| 17 | QDFX | Intuit | Quicken Financial Exchange Format |
| 18 | QDL | N/A | QDL Program |
| 19 | QDT | Quark, Inc. | QuarkXpress Auxiliary Dictionary Format |
| 20 | QEF | Microsoft Corporation | Microsoft Excel Query |
| 21 | QEL | Intuit | Quicken Electronic Library |
| 22 | QFD | Intuit Inc. | Quicken Data |
| 23 | QFI | Intuit Inc. | Quicken 2002 Data |
| 24 | QFILTER | Apple, Inc. | Mac OS X ColorSync Filter |
| 25 | QFX | Intuit | Quicken Financial Exchange Format |
| 26 | QHF | Ilgam Zulkorneev | QIP Saved History |
| 27 | QIC | Microsoft | Windows Backup Format |
| 28 | QIF | Intuit | Quicken Interchange Format |
| 29 | QIT | N/A | QIT Trojan Horse Format |
| 30 | QIZ | MacKichan Software | Exam Builder Quiz |
| 31 | QLGENERATOR | Apple | Quick Look Generator Format |
| 32 | QLI | Gammil, Inc. | Statler Stitcher |
| 33 | QM | Nokia | Qt Compiled Translation Source Format |
| 34 | QOB | Intuit Inc. | QuickBooks 2010 Pro |
| 35 | QPB | Intuit | QuickBooks Point Of Sale Data Format |
| 36 | QPH | Intuit | Quicken Price History Format |
| 37 | QPW | Corel | Quattro Pro Spreadsheet |
| 38 | QRS | Corel Corporation | Corel WordPerfect Equation Editor Support |
| 39 | QRY | N/A | Query Format |
| 40 | QSD | Intuit | Quicken Data Format |
| 41 | QSK | Quinnware | Quintessential Player Skin |
| 42 | QT | Apple | Apple QuickTime Movie |
| 43 | QTI | Apple | QuickTime Image Format |
| 44 | QTIF | Apple | QuickTime Image Format |
| 45 | QTK | N/A | Apple QuickTake Picture Image |
| 46 | QTX | Apple | QuickTime Extension |
| 47 | QTZ | Apple | Quartz Composer Format |
| 48 | QUA | Avira Operations | Avira AntiVir Quarantined Format |
| 49 | QUD | Quark, Inc. | QuarkXpress Auxiliary Dictionary |
| 50 | QUICKEN2015 | Intuit | Quicken 2015 Data File |
| 51 | QUICKENBACKUP | Intuit | Quicken Essentials For Mac Backup Format |
| 52 | QVM | id Software | Quake 3 Virtual Machine Format |
| 53 | QXD | Quark Software | QuarkXPress Document |
| 54 | QXF | Intuit | Quicken Essentials For Mac Exchange Format |
| 55 | QXP | Quark Software | QuarkXPress Project Format |
| 56 | QXT | Quark Software | QuarkXPress Template |
