Import an .stl or .obj file into Meshmixer.
Notes
If you already have a file open in Meshmixer you can drag more files into the window. The program will ask if you want to Replace or Append. Choose Replace if you want to replace the old file with the new, or Append if you want to add the new file to the old.
You can also load multiple files into the program at a time by highlighting both.

