I have a mac air and an iMac and both have Pages. I use Pages on my air and save all documents to iCloud. I can see them on my iMac but it won't open with Pages. It becomes visible if I change it to open with preview but I can't interact with it.

I have an mac air and an iMac 5k - pages runs on both. I use pages on my air and save all my documents to iCloud drive. I can see the documents on my iMac but some won't open in pages which is bizarre? They will open if I change it to open with preview but then all I can do is read it - I can't add to the document - All I want is to be able to see all my documents on all my devices and to be able to have them sync so I can add to the documents from any of my devices. I also have an iPhone 6 and an iPadair2 but I would be happy just to have the iMac and macair sync for starters. I have folders within folders in my documents,. The folders which contain pdf's and individual files open OK . The one I am having difficulty with is the file which I use for ongoing correspondence - in other words it is quite long - I keep adding to it ( by copying letters in and letters out so I can see a sequential history of what has been going on by scrolling down ) in date order so that it could be 1 - 100 pages long - but I don't think the size is a problem. I don't understand why some folders can open and others not . Has anyone any suggestions please. I have been trying to get this to work for months since iCloud drive came in. It has got much better but it is still not good enough - or maybe it's me?