When simply you add a file to a project, the wav file remains the same.
Any changes made in the object editor are all virtual (non-destructive).
The offline functions, it seems, can be either virtual or destructive. They give you a choice.
To check, what I did was to make a copy of the file, and then use the dos file compare "fc" command to compare the files. (After doing a "virtual" normalization).
I have also noticed that if you import audio using the import function that it appends some "Samplitude" specific info to the end of the file. (You can see that with Ultraedit). Some "list" chunks and "data" chunks, etc.