Hi Q,
Pages is not MS Word.
MS Word is not Pages.
The two applications use different methods to control the way information is displayed on the screen and on the page.
Features present in one of these applications may be missing from the other, or supported in a different manner in the other.
Exporting a file from Pages to the file format used by MS Word dumps any features that are not supported in Word.
Importing a Word format file into Pages omits any features used in the Word document that are not supported in Pages.
Simple documents (simple in the sense that they use few or no features not supported at the 'other' end) will translate accurately. More complex ones will not.
If transfer of your documents between you and one or more others using MS Word, your best course is to choose a tool that will do the job more accurately.
MS Word is available as part of MS Office Mac. It's feature set does not match exactly the features of the Windows version of Word, but the match is much closer.
Or you could try LibreOffice or Apache OpenOffice, both intended to more closely match the features of Word. Both are free to download and to use (although both do request donations to support future development). The links take you to the applications websites.
Regards,
Barry