It depends. For example, if the visitor has Adobe Acrobat plugin installed, the PDF will display in browser window.
https://helpx.adobe.com/acrobat/using/display-pdf-in-browser.html
If they don't, then the PDF will download when they "open" it. There is a Javascript plugin that allows viewing PDF files directly in browser, that I might consider including in Files app:
https://github.com/mozilla/pdf.js / [demo]
As for Word, no I don't think it's possible to display in browser window. At least there is no Word browser-plugin, and it's not possible with Javascript. There is a solution noted on the below link, which involves loading the Word document via Google docs. Could be interesting, but it's not a direct solution.
https://stackoverflow.com/questions/27957766/how-do-i-render-a-word-document-doc-docx-in-the-browser-using-javascript
By default, PDF and Word are not supported by most browsers and will simply force download.