Autodesk AutoCAD is probably the only software used to export DWG drawing as BLK file. This is usually done for publishing purposes.
Convert AutoCAD drawing to AutoCAD block template file.
We found 2 software records in the database related to .dwg to .blk file format conversion.
Microsoft Windows software - convert dwg to blk on Windows
Leading 2D and 3D CAD development software from Autodesk
Convert from dwg file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned dwg to blk. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert dwg to blk on OS X
Mac version of popular Autodesk AutoCAD software