Perhaps for the macOS (OS X 10.11) you are using on your MacBook Air, the Pages application is up to date and cannot be further updated to the latest version.
The Pages document you received by email might be from a more recent version of Pages than the one you are using, and hence, it might not be compatible (will not open).
You may have to upgrade your mac OS (Operating System) to be able to update Pages further. If you would like to do this (it is a free upgrade):
macOS - How to Upgrade - Apple
Alternatively, as a work around, you can use Pages on iCloud.com. Log on to iCloud.com, sign in. Launch Pages on your web browser. Then you can upload the Pages document you received by email, and it should open there. Here are the steps:
- Save the Pages document you received by email, on your MacBook Air Desktop.
- Go to icloud.com, you can log into your Apple iCloud account from Safari Web Browser.
- On iCloud.com (Safari), launch the Pages app.
- At the top of this page, and every other page where you’re able to upload files within the iCloud web interface’s apps, you’ll see a cloud-shaped icon with an up-facing arrow going through it.
- This is the upload icon, and clicking it on it will bring up a prompt to search your system and upload a new file. Navigate to your desktop and select the Pages document (email attachment - you have already saved there from Step 1.)
This will upload the document to Pages on iCloud and (hopefully) open it!
Good Luck!