To create collage in  ACDSee Ultimate version, you can use the following steps:
  1. In the Manage mode. Click File | New Image and then choose your size from background options.
  2. That will bring you to the Edit mode, then click on the Layer menu on top left to Import from file
  3. Resize the imported image and place it on your background.
  4. The import from file again for the next image - resize by dragging the corner and so on....
  5. Save as either an acdc format or jpeg