A family of Microsoft word processing software products for creating web, email, and print documents.
Check the settings for the paragraph styles in the affected document. In particular, see if the Normal style somehow has incorporated italic.
It is possible for the Normal style to include italic while that attribute is suppressed in the document because the person who designed the document template has turned off the italic for selected text.
In the Styles pane (Ctrl+Alt+Shift+S), rest the mouse pointer on the Normal style, click the little arrow and choose Modify from the drop down menu. Verify the style settings.
Repeat these steps with other styles if necessary.