Reality: False. Creating a .bak takes milliseconds because it’s just a file rename operation, not a compression or encoding process. The performance hit is unnoticeable.
.DWG (Drawing) is the proprietary binary file format used by AutoCAD and compatible CAD software. It is the industry standard for storing 2D and 3D design data. It contains geometry, layers, metadata, and references. This is your "live" working file. .bak to .dwg
If renaming the extension results in this error, it is possible the file is not a standard AutoCAD backup. It could Reality: False
Even though you opened it via the interface, you still need to perform a "Save As" to create a permanent .DWG file. Go to File > Save As and ensure the file type is set to the latest .DWG format. This is your "live" working file
You can batch-convert many .bak files to .dwg using the Windows Command Prompt.