From the article:

The [<file-preview>] component takes one attribute, file-id, which points to the ID value of the field to monitor. As for preview support, I figured I could cover these:

• Images (of course)

• HTML, .txt

• Markdown (after converting to HTML)

• Office docs (Using the excellent officeParser library)

• PDF (ditto)

• Audio and Video (using the browser's built-in support)