When Pages crashes, it should offer to send the report to Apple. Do that, as there are Apple Pages engineers that will review this and make sense of it. We are fellow users, and usually, the output of Pages crashes is useless to identifying the actual cause. It might be a missing font that Pages requires, it might be some other obscure Pages issue, or the application itself has been damaged by anti-virus, or so-called cleaning applications, that may have removed part of the internal application content.
Once Pages has crashed, it will continue to attempt to load its last saved state each time you launch it, probably resulting in another crash. You need to break this chain, by pressing the shift key while launching Pages. This is not a cure-all either, if there is something truly wrong.
I would boot your Mac into Safe Boot mode, and use Pages there for awhile to see if the crashes continue. Try different documents too. Safe mode also clears out System caches, and rebuilds the System font database, which may also be a blessing in disguise. After rebooting normally from Safe Boot mode, see if Pages has returned to normal operational behavior. There may need to be other steps taken if it continues crashing.