My son added Pages back when he was living at home and using my laptop. He now has his own and I still use Pages. I would like to update it as it has been a few years without updates now. I am even happy to pay for it again since he is probably using it on his laptop too from his cloud. But I don't want to lose my current documents. What do I do? I cannot update using my Apple ID and it will not let me purchase it since it is already on the computer. Does this question even make sense?
You'll not lose any of your documents if you delete the Pages Application from your Mac and, then, buy it again using your own AppleID. This is because documents are stored on as individual files on your computer not within the Pages application.
If you want to update the current installation, you have to use the AppleID that your son used to install it.