From what it seems, the Mangal font is set as the default one. In order to fix this, press Alt + Ctrl + Shift + S key combination and click the Manage Styles icon. Select the Set Defaults tab and change the Mangal font to the desired one. Also, click the Word icon, select Word Options and press Proofing. Click AutoCorrect Options and change the format settings from AutoFormat and Auto Format As You Type tabs. For further details, check Microsoft Support page.