What does message "required index.xml file is missing" mean

What "documents" exactly?

Verify the exact words = verbatim = of the error message and exactly when it occurs.

Tell us a Story - with a beginning, a middle and end. We need to understand everything that you know and have experienced.

If this issue is new, tell us what immediately preceded its onset - add software, upgrade or update? New equipment?

Quoted from  Apple's "How to write a good question"

To help other members answer your question, give as many details as you can.

• Include your product name and specs such as processor speed, memory, and storage capacity. Please do not include your Serial Number, IMEI, MEID, or other personal information.
• Provide the version numbers of your operating system and relevant applications, for example "iOS 6.0.3" or "iPhoto 9.1.2".
• Describe the problem, and include any details about what seems to cause it.
• List any troubleshooting steps you've already tried, or temporary fixes you've discovered.

For a detailed "coaching", please see the User Tip > "Help us to help you on these forums"<https://discussions.apple.com/docs/DOC-5431>

"Keep It Short and Simple" - Take your time... but be thorough - ÇÇÇ

Exact same thing is happening to me. I upgraded to Yosemite 10.10.3 and ever since, any Pages document that I try to open generates that pop-up window with the error message. This happens with Pages documents I have created on my MacBook Pro (Retina, 15-inch, Early 2013) as well as any Pages document created on my husband's or my iPad and emailed to me.

See if the comments in pages file is missing its index.xml file? are helpful... especially Pert Breis's - ÇÇÇ