This is a bug 'fixed' version of the original io_anim_c3d for Blender 4.1
To use the addon for importing .c3d files - download this git repo as a .zip file and import it via Edit > Preferences > Addons > Install
- Make sure the add-on is installed and enabled (see the 'How to Install' section).
- Go to File->Import->C3D (.c3d) to open the import window.
- Change the import settings (if needed).
- Navigate to the folder containing the .c3d file, and...
- Double-click to import a single file or
- Select file(s) to import and click the 'Import C3D' button.