Here's a common practice: You open an existing document in Microsoft Word, Excel or PowerPoint, make some changes to it, then save it using a different filename. That leaves the original alone, but gives you a modified copy.
Just one problem: Microsoft's Office 365 no longer works that way. Because of an incomprehensible change pushed out not long ago, any changes you make are automatically saved -- meaning your original document is overwritten, even if you don't want it to be.
What's more, when working on a document that's already been saved at least once, you'll notice that the "Save As" option -- as old as the software itself -- has disappeared from the File menu.
What the heck, Microsoft?
This is especially frustrating because the update was pushed out without warning, explanation or instruction. It just happened one day. To me it seems borderline insane that Microsoft would change a fundamental method of saving Office documents without adequately informing users.
It gets worse: Although you can easily turn off the new AutoSave feature by clicking the little toggle in the upper-left corner of the screen, that turns it off only for the current document. There's no way to globally disable AutoSave.
What you can do is turn off AutoRecover, the feature that automatically creates a backup at regular intervals. That effectively disables AutoSave -- while also leaving you without the aforementioned backup.
If you're willing to do that, click File > Options > Save, then clear the checkbox next to "Save AutoRecover information every X minutes."
There's another way to work around this, but it means changing the way you work, and probably have worked for decades. Microsoft recommends that when you open an existing document with the intention of saving it with a different filename, you use the new "Save a Copy" option (which is what replaced "Save As") before you make any changes.
Ugh. What if I make changes and then decide to abandon them? Now I've got an unnecessary, unwanted copy I have to manually delete.
I wouldn't be so miffed about this if Microsoft had notified me first. Plenty of web and mobile apps present users with informative overlays when introducing them to new features. Why can't Office 365 work the same way?
If you're equally miffed, there's one more option: You can disable AutoSave by tweaking the Windows registry. That's according to a Microsoft support article. Unfortunately, the hack works only in Office 365 ProPlus. I tried to find those same registry entries in Office 365 Home and came up empty.