This is how I can do it:
1. Long-press an empty part of the homescreen, then select Add Widget.
2. Scroll to Total Commander, and drag and drop the Total Commander widget to the location on the homescreen you want the link.
3. When you release, it will ask you to choose a file or folder -- navigate to the folder with your file, then tap the file.
4. In the next window, tap the arrows to the right of the "Command" field, and choose the app to open that file when the widget is tapped.
Does that work?