Checked against the current Windows build. Where an article names a menu, a button or a message, that is the wording in the application, not a paraphrase.
What a crash actually costs
Edits live in memory until you save them. If the application stops — a crash, a power cut, a forced restart — everything held in the session goes with it, including a signature you made against a hardware token a minute earlier. There is no journal and no recovery file, so there is nothing to offer you when it starts again.
That is a choice rather than an oversight. An autosave would have to write to a file you had not chosen, which is the behaviour the session model exists to avoid, and a recovery file would be a copy of your document sitting somewhere you did not put it. When the application does stop, a dialog says so: that what you had not saved is gone, that no file of yours has been changed or damaged, and that nothing has been recorded anywhere about what you had open. We collect no telemetry. Windows itself can send a crash report to Microsoft that may contain part of the document that was open, and that is not ours to switch off.
The dot on the tab and the banner under it
A document with unsaved changes shows a dot before its name in the tab strip, the way every editor marks one. Above the pages, a banner counts them: “3 changes, not saved. They are held here; the file on disk is untouched.” Where the last change could not keep something — a substituted font, a block that grew past what was under it — a second line in the same banner says what.
The banner also carries the buttons that act on the session: Undo, Redo, Discard, Save a copy and Save. Ctrl+Z, Ctrl+Y, Ctrl+S and Ctrl+Shift+S do the same jobs from the keyboard. Discard asks before it acts, and says whether it is putting you back to the file you opened or to whatever was last written — two different answers, once you have saved during the session.
Closing asks, in both places
Closing a tab that has unsaved changes raises a question naming the document and the number of changes, with “Close without saving” and “Keep it open” as the two answers. Closing the window does the same for however many documents are dirty, listing them by name when there is more than one.
Opening a file that is already open counts as closing it. Re-opening a path refreshes it from disk, which is what you want after an operation has written that file and a silent destruction of your work when the tab held unsaved changes, so the same question comes first. Read it rather than dismissing it: “Close without saving” means exactly what it says, and there is nowhere to get the changes back from afterwards.
Save, Save a copy, and where the session points next
Save replaces the document you opened. Save a copy asks for a name, leaves the original alone, and then follows the session onto the new file, so your next Save writes to the copy rather than to the file you started from. That is deliberate: somebody who has chosen a new name is working on that file now, and leaving the session aimed at the old one is how a later Save destroys the thing the copy existed to protect.
If you would rather never overwrite anything, Settings has “Always save a copy, never replace the original”, which makes Save ask for a name every time. A signed document is a case of its own: an ordinary save rebuilds the file and the signature does not survive that, so a red banner says so before you choose, and Save a copy leaves the signed file as it stands.
Working with a session that lives in memory
The practical consequences are small and real. On a long job — OCR over a hundred pages, a run of page edits, a form filled from a paper original — save a copy at the points you would not want to repeat, rather than treating a whole afternoon as one session. Name those copies so they cannot be confused with the original at a glance.
Not everything is a session. Compression, conversion, image export, split and the other operations that produce a file ask for an output path first and write it when they finish, so those results are on disk whatever happens next. What the application itself keeps on your machine is one settings file: no cache, no recent-file list, no log, no index and nothing in your temporary folder. The privacy page has the rest of that.
The two places worth looking next.
Read the matching guide if you want the reasoning rather than the fix, and check limitations before spending any longer on it — some of what people look for here is absent on purpose.