You can change the Advanced setting that automatically converts A4 to Letter in Microsoft Office Word.

1. Open Microsoft Office Word.
2. Click the Office button.
3. Click Word Options.
4. Click Advanced.
5. Scroll down to the Print section.
6. Clear the Scale content for A4 or 8.5x11" paper sizes option.
7. Click OK in the Word Options window.
8. Restart Microsoft Office Word.