What is the STC file format?
An .stc file is a legacy spreadsheet template created by StarOffice and carried into the OpenOffice.org 1.x series. It stores a pre-configured Calc spreadsheet used as a base for new documents - carrying page formatting, cell styles, fonts, margins, named ranges, and chart definitions without containing actual data.
The format dates from the late 1990s StarOffice era. It was superseded in 2005 when OpenOffice 2.0 introduced the OpenDocument Format, replacing .stc with .ots (OpenDocument Spreadsheet Template) and .sxc spreadsheets with .ods. Modern LibreOffice and Apache OpenOffice still open .stc files for backward compatibility but save templates as .ots.
.stc uses a proprietary binary container distinct from both OLE2 (used by Microsoft Office formats) and ODF XML. The internal structure is not publicly documented. Password protection was available in StarOffice for sensitive templates.
.stc is not to be confused with Microsoft Excel's .xlt / .xltx template formats - all serve the same spreadsheet-template purpose but are mutually incompatible. If you need to reuse an .stc template today, LibreOffice Calc is the most accessible tool; open the file and re-save it as .ots for ongoing use.
Security & safety
RISK: LOWLegacy binary template file; no known macro execution in STC format. Unlike modern Excel templates (.xltm), STC does not support embedded macros in any documented way. Low risk format.
Format details
in a nutshellPrograms that open STC files
Windows2 apps
Apache OpenOffice
Open-source File > Open, select the .stc file. It opens as a template; File > Save As to convert to .ots or .xlsx. 
LibreOffice Calc
Open-source File > Open, select the .stc file. LibreOffice reads the legacy format with backward compatibility. 
macOS2 apps
Linux2 apps
Technical details
deep spec| Document type | Spreadsheet template - stores styles and formatting as a base for new spreadsheets, contains no end-user data |
| Container | Proprietary StarOffice binary format - distinct from OLE2/CFBF and ODF XML |
| Era | StarOffice / OpenOffice.org 1.x series (late 1990s to 2004) |
| Superseded by | .ots (OpenDocument Spreadsheet Template) since OpenOffice 2.0 (2005) |
| Encoding | Binary, little-endian |
| Stored content | Page layout, cell styles, fonts, margins, named ranges, chart templates |
| Encryption | Optional password protection available in StarOffice |
| Spec availability | Internal structure not publicly documented |
| Backward compatibility | LibreOffice and Apache OpenOffice read .stc files; save as .ots for ongoing use |
| Related active format | .ots (ODF template); .ods (ODF spreadsheet document) |
| Associated OS | Windows, Linux, macOS |
| Magic bytes | None documented; no confirmed fixed byte signature |
| Development status | Format frozen; no current software generates new .stc files |
| MIME type | application/vnd.sun.xml.calc.template |
| Released | late 1990s (StarOffice era) |
STC conversions
Community Q&A
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