Sharing Pages documents

So I received a .docx word document form which I wanted to fill out and return. I initially opened the document in Pages on my Mac, and then through iCloud sharing completed it on my iPad, as I found the table easier to navigate on iPad.
However the person I sent it back to said that the email attachment is showing up for him as a zip file rather than the docx file, and even when he unzips it, there is nothing there.
Has anyone come across this? What is best practice for sharing documents that you have edited in Pages?
Many thanks,
Dave