Save edits and keep the original
Save an edit into the photo file, or as a new copy, and bring the untouched original back whenever you like: Portman2 keeps it in the originals folder.
Nothing is written until you save. Four buttons at the foot of the sidebar decide what happens to the edit.
Save
Save (or Save all for a selection, or Ctrl+S) bakes the edit into the photo file itself. Before the first save, the untouched original is moved to the library's originals folder, and every later save renders from that original — so editing again never stacks one edit on top of another, and the original can always be brought back. While saving, the sidebar says what it is waiting for.
Some files cannot be written in place: RAW files, and virtual copies. The sidebar says how many and why; use Save as copy for those.
Save as copy
Save as copy writes a new file beside each original, in the same albums and with the same tags, and leaves the original file as it was.
Reset all
Reset all puts every setting back to neutral in the editor. It is not saved until you press Save.
Restore original
Restore original discards the saved edit and brings the untouched file back from the originals folder, after asking. It is only offered for photos that have been saved with an edit.
See Originals for where the originals folder is.