| sdh | SurveyPro SDH Data |
| sdi | Seadragon Index Data |
| sdif | Hy-Tek Meet Manager SDIF Data |
| sdinstall | Speckie Dictionary Installation Data |
| sdir | Logic Pro Space Designer Impulse Response |
| sdl | SmartDraw Library |
| sdl | Suunto Dive Log |
| sdltb | SDL MultiTerm Termbase |
| sdltm | SDL Trados Translation Memory |
| sdlxliff | SDL Trados XLIFF Localization |
| sdm | BrainVoyager QX Design Matrix |
| sdm | STATISTICA Workspace |
| sdmx | Statistical Data and Metadata eXchange Dataset |
| sdo | DB/TextWorks Database Deferred Update Directory |
| sdpa | SDPA Data |
| sdpc | CoCreate SolidDesigner Data |
| sdtbx | XTRF Terminology Database |
| sdtid | RSA SecurID Software Token Import Data |
| sdts | Spatial Data Transfer Standard File |
| sdv | WDK Static Driver Verifier Rules |
| 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 |
| searchconnector-ms | Windows Search Connector Data |
| seawifs | SeaWiFS Data |
| sec | Migration Wizard Secondary IFF File |
| sec | PTC Creo Section Data |
| 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 |