Via Microsoft Office Online Server
You can edit the following file types in Offline Office within the portal:
Word files – .docx, .docm, .odt, .doc – When editing any Word file, the file is saved as a .docx file.
Excel files – .xlsx, .xlsb, .xlsm, .ods, .xls – When editing any Excel file, the file is saved as a .xlsx file.
PowerPoint files – .pptx, .ppsx, .odp, .ppt – When editing any PowerPoint file, the file is saved as a .pptx file.
Via Portal Preview Server
The following file types are supported:
Document – DOC, DOCX, XLS, XLSX, PPT, PPTX, RTF, CSV, PDF, ODT, ODS, ODP, and many older document formats
Web – HTML, SVG
Image – TIFF, JPG, JPEG, JP2, GIF, PNG, RAS, CAL, MIL, DIB, BMP, PSD, PCT, PCX, DCX, PCD, WMF, EMF, TGA, and many more image formats
Medical Image Files – DICOM, DCM
CAD – DGN (support for V7 and V8 DGN, including V8 XM and V8I), DWG (version 2.5 through 2014), DXF (version 2.5 through 2014)
Email – EML, MSG
Other – txt