Can I install apache open office on my iPad?

Mac computers and iPads use different operating systems. Software designed to work on the Mac OS will not run on an iPad which uses iOS.

That app is not available from the App Store for iOS based devices such as your iPad but there are other word apps for iPad to choose from.

Microsoft Word, Excel, Powerpoint are available to download are are free to use on an iPad Air. https://itunes.apple.com/us/app/microsoft-word/id586447913?mt=8

Google

Docs

"Open, edit, and save Microsoft Word documents. Share documents and work together with others in the same document at the same time."

https://itunes.apple.com/us/app/google-docs/id842842640?mt=8

Sheets

"Open, edit, and save Microsoft Excel files. Share spreadsheets and work together with others in the same spreadsheet at the same time."

https://itunes.apple.com/us/app/google-sheets/id842849113?mt=8

Slides

"Open, edit, and save Microsoft PowerPoint files. Share presentations and work together with others in the same presentation at the same time."

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Apple Pages, Numbers and Keynote for iOS.