How do I share a pages file with a windows user?

As only Pages can open Pages documents and Pages is not available on Windows, the interoperable media would need to be either Word (.docx), or PDF, depending on whether the recipient planned to change, or just read the content. In either case, they will need an appropriate application to open the document format you have sent.

In Pages v13.1 for iPadOS 16.5.1, you would start with the open Pages document. Click on the document name and on the resulting secondary menu, choose Export and your choice of Word or PDF. A Share panel will then pop up where you can select Mail. The exported document type will be attached to a new Mail compose window and you can enter the recipient's email and a subject line, then send the email.