What is the BLK file format?
.blk files are associated with the AutoCAD software package, specifically its Publish and Attribute Extraction workflows.
A .blk file is a saved template that defines which AutoCAD block definitions and their properties should be included when publishing a drawing to DWF, PDF, or DWFX, or when extracting attribute data to a spreadsheet or table. It stores the selection of block names and attribute columns - not the drawing geometry itself, which lives in the .dwg file. .blk files are small, plain-text files generated by AutoCAD's Block Template dialog or Attribute Extraction wizard.
Block template files are typically used when multiple drawings share block definitions that differ only in certain attribute values. The template controls which attributes get exported or published, letting teams apply the same repeatable extract configuration across related drawings without reconfiguring it each time. This modularity allows AutoCAD to re-use the template across a project efficiently.
One other use of .blk files is controlling project data distribution and sharing. Complex projects commonly require only certain parts - specific sections, modules, or attribute views - to be shared among team members. A .blk template specifies exactly which block properties are exposed when a drawing is published to a sharable format, making it straightforward to restrict what information leaves the project.
Security & safety
RISK: LOWAn AutoCAD Block Template is a small, passive text/template file with no executable content, so it is low risk to handle. The only real caution is the overloaded extension: a .blk from a game or a backup/virtualization tool is an entirely different (binary) file, so confirm the source before assuming it is an AutoCAD template. Avoid sketchy "BLK opener" download sites that bundle adware - for the AutoCAD type, AutoCAD itself is the tool.
Format details
in a nutshell- Hexen / Doom-engine BLOCKMAP (.blk) - Game map block/collision data used by some Hexen and Doom-engine tools - unrelated to AutoCAD.
- VirtualBox / disk block file - Some virtualization and backup tools name raw block-image chunks .blk - unrelated binary data.
Programs that open BLK files
Windows2 apps
AutoCAD
Paid Use the Block Template dialog (Publish) or Attribute Extraction wizard to create/load the .blk template; it is used within AutoCAD, not opened as a standalone document. 
Notepad++ / VS Code (inspect only)
Open-source Open the .blk as text just to read the saved block/property selection. Editing by hand is not recommended - regenerate it in AutoCAD. Technical details
deep spec| File type | Plain-text AutoCAD template (not a drawing) |
| Developer | Autodesk |
| Encoding | ASCII / UTF-8 plain text |
| Typical size | 1 KB - 50 KB |
| Associated OS | Windows (primary AutoCAD platform for this workflow) |
| MIME type | text/plain |
| Purpose | Defines which block definitions and attribute columns to include in a Publish or Attribute Extraction operation |
| Geometry storage | None - drawing geometry stays in the .dwg; this file is a selection filter only |
| Creation tool | Generated by AutoCAD's Block Template dialog or Attribute Extraction wizard |
| Reusability | A single template can be applied across multiple drawings that share the same block definitions |
| Publish targets | DWF, DWFX, PDF (the formats a drawing is published to when using the template) |
| Manual editing | Can be inspected in any text editor (Notepad++, VS Code); not intended for manual editing |
| Released | AutoCAD (modern BLK template used with Publish / Attribute Extraction workflows) |
| Latest version | Tied to the AutoCAD release that created it (AutoCAD 2019-2026 use the same template concept) |
| Specification | help.autodesk.com |
BLK conversions
Community Q&A
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