It's best to save a word file to PDF but only after the word file has been properly configured for accessibility.
Word files present a security issue because they are much more easy to edit and alter once downloaded than PDF files, so if for some reason it's not possible to create a PDF and the content is required to be delivered in a regulated format, apply security settings to the Word File, using Word's document protection.
Accessible Word Document Requirements
A Word document is accessible if:
Word 2010 comes with an accessibility checker that can help find a few overlooked accessibility items in a document, but it will not locate most problems. To run Microsoft Word's accessibility checker, select File, then click the Info tab on the left-hand side of the screen. Then click on the Check for Issues button and select Check Accessibility.