I just realised that I never moved the SweetHome3D app from the downloads to the applications and assumed I did so I tried opening the file with a similar application...

*facepalm* Thanks anyway

Yesterday, I worked on a room as a part of a project and saved multiple times during the process of making it. Today, I tried opening the file and an error came up, saying that the file could not be opened. The product is good and really helped me but there's a serious problem when a file can't be ...