For anything in assets, use asset.get. So your freemarker would be ${asset.get("/html/assets/MyFile.pdf")}, which will automatically generate the full URL for you.
The other benefit to using asset.get is it will generate a URL that leverages the CDN for the asset to improve performance.
Correction; I didn't fully read your post.
Somewhat confusingly, the value in ${ } needs to reference a text key, and can't actually parse freemarker.
If you want to link to that file in your ToS, you're probably better off just making a relative link directly to it, e.g. <a href="/html/assets/MyFile.pdf">Link Here</a>
But, if you were actually in Freemarker land, you would use asset.get as I noted before.
