How can I change a document to Word format to send to someone?

Adding to what FoxFifth said…

Be aware that the translation from Pages to Word may not be 'perfect.' Any Pages features not supported in Word (or supported differently in Word) will result in a document with a different appearance (and possibly less content) in Word than it had in Pages.

The same is true of Word documents opened in Pages (and translated by Pages into Pages documents).

For very simple documents, the process is reasonably accurate; as complications are added, this becomes less so.

If you are regularly exchanging documents with Word users, and find the translations unacceptable in either direction, you may find it better to create those documents in MS Word for Mac, or in LibreOffice, a free application intended to more closely match the features of Word.

Regards,

Barry

Pages File menu > Export to > Word.