| sdxf | Structured Data eXchange Format Data |
| sdxm | SDX Signed Data |
| sdxx | Autodesk AutoCAD Civil 3D Survey Database Extended Properties |
| sdy | Starmoney Database File |
| sea | MAXQDA Saved Search |
| seawifs | SeaWiFS Data |
| sec | Migration Wizard Secondary IFF File |
| seco | MSX Configurator Software Update |
| secstore | Adobe Acrobat Security Store File |
| see | LISCAD Database |
| seg | Mail.dat Segment File |
| seg2 | SEG-2 Data File |
| segd | SEG-D Data File |
| segy | SEG Y Data File |
| sel | LinkOne Selection List |
| sem3d | SEMulator3D Model Data |
| semul | WinZip Registration Data |
| senl | SAP Enable Now App Launcher |
| sep | SEEP/W Data |
| sep | SimEnhancer Profile |
| seq | Workswell Recorded Thermal Sequence |
| seq | CYANA Sequence File |
| seq | Tinker Sequence |
| server | Bonobo Activation API Data |
| ses | SPECCTRA Session File |
| ses | Adobe Audition v2 Session |
| sesx | Adobe Audition Session |
| set | PLINK END-terminated Variant Set Membership List |
| sew | Janome Stitch-based Embroidery Data |
| sez | SEEP/W ZIP Compressed Data |
| sf | StatGraphics Centurion Data |
| sf0 | Windows Sytem File Check Data |
| sf1 | Census Bureau Summary File 1 |
| sf2 | SAS Consolidation Database |
| sf3 | StatGraphics Centurion Data |