| Extension | File Description |
| .ARM | Uncommon Files |
| .ARMADA | Uncommon Files |
| .ARMOURFONT | Uncommon Files |
| .ARMX | Uncommon Files |
| .ARMY | Uncommon Files |
| .ARN | Uncommon Files |
| .ARO | Web Files |
| .ARP | Settings Files |
| .ARPX8 | Uncommon Files |
| .ARQ | Uncommon Files |
| .ARR | Raster Image Files |
| .ARS | Settings Files |
| .ART | Developer Files |
| .ARTGALLERY | Uncommon Files |
| .ARTICLE | Uncommon Files |
| .ARTICLE1 | Uncommon Files |
| .ARU | Uncommon Files |
| .ARV | Uncommon Files |
| .ARW | Raster Image Files |
| .ARX | Plugin Files |
| .ARY | Uncommon Files |
| .ARZ | Uncommon Files |
| .AS | Data Files |
| .AS0 | Uncommon Files |
| .AS1 | Uncommon Files |
| .AS2 | Uncommon Files |
| .AS3 | Uncommon Files |
| .AS4 | Backup Files |
| .AS5 | Uncommon Files |
| .AS6 | Uncommon Files |
| .AS7 | Uncommon Files |
| .AS8 | Uncommon Files |
| .AS9 | Uncommon Files |
| .AS? | Backup Files |
| .ASA | Web Files |
| .ASAX | Web Files |
| .ASB | Executable Files |
| .ASC | Text Files |
| .ASCII | Text Files |
| .ASCX | Web Files |
| .ASD | Audio Files |
| .ASE | Audio Files |
| .ASF | Video Files |
| .ASG | Uncommon Files |
| .ASH | Misc Files |
| .ASHDISC | Disk Image Files |
| .ASHDISK | Uncommon Files |
| .ASHPRJ | Data Files |
| .ASHX | Web Files |
| .ASI | Developer Files |
| .ASIC | Uncommon Files |
| .ASJ | Uncommon Files |
| .ASK | Database Files |
| .ASL | Settings Files |
| .ASLQUERY | Uncommon Files |
| .ASM | Data Files |
| .ASM1 | Uncommon Files |
| .ASM2 | Uncommon Files |
| .ASM3 | Uncommon Files |
| .ASMDAT | Uncommon Files |
| .ASMVERS | Uncommon Files |
| .ASMX | Web Files |
| .ASN | Uncommon Files |
| .ASN1 | Uncommon Files |
| .ASND | Data Files |
| .ASO | Uncommon Files |
| .ASP | Web Files |
| .ASPHTML | Uncommon Files |
| .ASPI | Uncommon Files |
| .ASPR | Uncommon Files |
| .ASPX | Web Files |
| .ASQ | Uncommon Files |
| .ASR | Data Files |
| .ASS | Misc Files |
| .ASSIGNED | Uncommon Files |
| Extension | File Description |
| .ASSOC | Uncommon Files |
| .AST | Settings Files |
| .AST2 | Uncommon Files |
| .ASTROGS | Uncommon Files |
| .ASU | Uncommon Files |
| .ASV | Settings Files |
| .ASW | Uncommon Files |
| .ASWCS | Settings Files |
| .ASWS | Settings Files |
| .ASX | Video Files |
| .ASXML | Uncommon Files |
| .ASY | Vector Image Files |
| .ASZ | Uncommon Files |
| .AS_ | Uncommon Files |
| .AT | Uncommon Files |
| .AT0 | Uncommon Files |
| .AT1 | Uncommon Files |
| .AT2 | Uncommon Files |
| .AT3 | Audio Files |
| .AT4 | Uncommon Files |
| .AT5 | GIS Files |
| .AT6 | Uncommon Files |
| .AT7 | Uncommon Files |
| .AT8 | Uncommon Files |
| .AT9 | Uncommon Files |
| .ATA | Uncommon Files |
| .ATB | Uncommon Files |
| .ATC | Settings Files |
| .ATD | Uncommon Files |
| .ATE | Uncommon Files |
| .ATF | Settings Files |
| .ATG | Uncommon Files |
| .ATH | Settings Files |
| .ATHEME | Uncommon Files |
| .ATI | Uncommon Files |
| .ATJ | Uncommon Files |
| .ATK | Uncommon Files |
| .ATL | Uncommon Files |
| .ATLT2 | Uncommon Files |
| .ATM | 3D Image Files |
| .ATMN | Uncommon Files |
| .ATMSPHR | Uncommon Files |
| .ATN | Settings Files |
| .ATO | Uncommon Files |
| .ATOM | Web Files |
| .ATOMCAT | Web Files |
| .ATOMSVC | Developer Files |
| .ATOOL | Uncommon Files |
| .ATP | Uncommon Files |
| .ATPZ | Uncommon Files |
| .ATQ | Uncommon Files |
| .ATR | Disk Image Files |
| .ATRAM | Uncommon Files |
| .ATROM | Uncommon Files |
| .ATS | Data Files |
| .ATT | CAD Files |
| .ATTR | Uncommon Files |
| .ATU | Uncommon Files |
| .ATV | Uncommon Files |
| .ATW | Uncommon Files |
| .ATX | Plugin Files |
| .ATY | Text Files |
| .ATZ | Misc Files |
| .AT_ | Uncommon Files |
| .AU | Audio Files |
| .AU0 | Uncommon Files |
| .AU1 | Uncommon Files |
| .AU2 | Uncommon Files |
| .AU3 | Developer Files |
| .AU4 | Uncommon Files |
| .AU5 | Uncommon Files |
| .AU6 | Uncommon Files |
| .AU7 | Uncommon Files |
| .AU8 | Uncommon Files |
| .AU9 | Uncommon Files |
