HOW CAN I INSTALL WORD DOCUMENT IN MY APPLE IPAD WITHOUT PAYING MONTHLY

MS Office for Windows and Macos is not free You have to pay to get it. There is no way around that. You can buy a standalone copy of Office, or you can subscribe to MS Office 365 to get it. But there is no free MS Office apps for MacOS.

You can use the web versions for free, but not the standalone copies you install on your computer.

The mobile versions for iOS and iPadOS are free and available in the App Store. If you have an iPad Pro, a MS 365 subscription is required.

Maybe a question for the Microsoft Product Help Communities.

If you just want a word processing app, you already have Pages installed and it's free.