What is the CTB file format?
.ctb is a binary file associated with AutoCAD, introduced with AutoCAD 2000 to replace legacy .pcp and .pc2 pen assignments. .ctb files store color-dependent plot style tables that control how a drawing prints, not how it looks on screen. Each table maps up to 255 of AutoCAD's indexed colors (ACI values 1-255) to output properties such as lineweight, screening, linetype, dithering, grayscale conversion, and pen number. These settings can be reused across different projects and applied to objects or layers.
.ctb files are stored separately from the .dwg drawing file and must be present in AutoCAD's Plot Styles folder for the drawing to plot as intended.
Newer versions of AutoCAD support a different plot style paradigm - styles assigned to named objects or layers rather than to color index numbers. For this purpose, .stb files are used instead of .ctb files. However, many projects still use .ctb files, mainly due to the high cost of rebuilding projects to accommodate the .stb format. A single project cannot use both .ctb and .stb standards simultaneously. Autodesk offers a built-in migration tool within AutoCAD for converting .ctb files to .stb format.
Security & safety
RISK: LOWA CTB is a passive settings file and cannot execute code, so it is safe to open. The only practical 'risk' is using the wrong CTB and getting incorrect prints (wrong lineweights/colors) - verify you have the CTB the drawing's author intended. Download CTBs only from trusted colleagues/standards, and place them in AutoCAD's Plot Styles folder, not random locations.
Format details
in a nutshell- COMSOL Multiphysics binary file - Some COMSOL exports use .ctb; unrelated to AutoCAD plotting.
- ChessBase / training database table - A minor, unrelated use of .ctb in some chess software.
Programs that open CTB files
Windows4 apps
AutoCAD
Paid Run STYLESMANAGER (or Plot dialog > Plot style table > Edit) to open the Plot Style Table Editor; edit per-color settings, Save As. Place the .ctb in the Plot Styles support folder. 
DWG TrueView
Free Free Autodesk app - drop the .ctb into its Plot Styles folder and select it when plotting a DWG to PDF. Best no-cost way to USE a CTB. 
Bricscad
Paid AutoCAD-compatible CAD - reads and edits .ctb plot styles in its own plot style manager. 
progeCAD / ZWCAD / GstarCAD
Paid Low-cost AutoCAD-compatible programs that import and apply CTB plot styles. 
macOS1 app
AutoCAD for Mac
Paid Plot Style Table Editor available; manage CTBs in the macOS Plot Styles folder. Technical details
deep spec| Developer | Autodesk, Inc. |
| Format type | Proprietary binary plot style configuration table |
| MIME type | application/octet-stream |
| File signature | PIAFV0 (ASCII, offset 0) |
| Encoding | Binary, little-endian |
| Color index entries | 255 (one per AutoCAD Color Index value 1-255) |
| Per-entry properties | Output color, lineweight, screening %, linetype, dithering, grayscale, pen number |
| Typical file size | 1 KB - 20 KB |
| Platform support | Windows, macOS (via AutoCAD for Mac) |
| Default storage location | AutoCAD Plot Styles folder (user profile or shared network path) |
| Automatic backup | AutoCAD saves a .ctb.bak copy when a table is overwritten |
| Compatibility range | AutoCAD 2000 through AutoCAD 2026 (format unchanged) |
| Named-style alternative | .stb files - styles assigned per object or layer, not per color index |
| CTB/STB coexistence | A single drawing project cannot use both standards simultaneously |
| Predecessor formats | .pcp and .pc2 pen assignment files (pre-AutoCAD 2000) |
| Released | 2000 (AutoCAD 2000 - replaced legacy .pcp/.pc2 pen assignments) |
| Latest version | Stable since AutoCAD 2000; unchanged through AutoCAD 2026 |
| Specification | www.autodesk.com |
CTB conversions
Community Q&A
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