A family of Microsoft word processing software products for creating web, email, and print documents.
Pages is the name of the Apple word processing program you used to create the document -- documents aren't saved in the program. Microsoft Office does not read files saved in any of the native iWork file formats.
You'll need to open the document in Pages then use the File> Export feature to save a copy in Word format.
Just in case you aren't aware of it, Pages & [any version of] Word do many things quite differently. If you intend to try maintaining a single file using both of the 2 programs you may have some challenges to overcome.
Regards,
Bob J.