Pages document opening old version from iCloud Drive; how to manage versions?

I came across something unfamiliar after reopening a Pages document I typically refer to and change, at least slightly, several times a day. The section I was looking for was missing. I thought I might have accidentally deleted it, but then I noticed that the date on the top of the document was almost two months ago. I go to the "date and time" menu every time I open any document and change it to today's date, so that was another clue something was wrong. I searched recently opened documents and found two versions of my file: the one I had just opened was flagged as being in iCloud Drive, and the other was a "mobile document." That was the correct, current version. I had never heard of mobile documents. Why do I have two versions, and how do I make sure I access the most recent? I usually store this document in the dock after I'm through editing, rather than permanently closing it, so maybe that's why I had never accessed an older version. I think this happened once before (that I know of) a few weeks ago, when I had the impression that recent edits and additions had vanished from another Pages document. It unnerves me to think that the Mac is dredging up old versions of my files, and that if I don't realize it could have multiple copies, all different, of what should be just one document. How do I manage this?