Hi 
Usually that is because the Windows side has Page settings set to "US Letter" whereas the Gnu&Linux size assumes the more international A4 as used by almost the entire rest of the world (incl Canada).
You might find other programs in Windows also assume "US Letter" and to affect all of them you might find changing your "Locale and Regionalisation" settings might help. Sometimes it is the printer that is set to "US Letter" and that might affect other machines that use the same printer. If you want to minimise the amount of change then in LibreOffice just go to
Format - Page - Page (2nd tab) - top drop-down lets you change paper-size
However i suspect that might only affect just the 1 single document.
Other reasons for the change is a change in the fonts used by Windows. Tim of Kracked Press once gave me a very much nicer version of Arial and on the few machines where i installed that people started using Arial more only to be slightly disappointed when viewing their documents on other machines that just had the default Arial. Gnu&Linux has a ton of fonts that are not installed by default on Windows (and similarly vice-versa) so changing OS means the document has to substitute for something similar but not quite the same. It's a pain. A lot of the fonts included by default in Windows have copyright notices but still allow you to install on Gnu&Linux. It's piracy (unless you have fulfilled the terms&conditions) but a lot of people do it and it's rare to get prosecuted for it. The Gnu&Linux fonts use "copyleft" (such as Creative Commons "CC-by-SA") and even encourages you to install anywhere you like.
Regards from
Tom 