The drop-down has web standard (included in pc/mac operating systems) and Google free fonts, which don't require a purchase or installation for web use.
Even some common fonts found on most PCs require a paid licence for web** (and print) use, they're included in your system for personal use.

Google fonts are added to a site by use of a simple link (which RSD does for you).

If it were possible, there are so many other considerations. Maybe the font you add is only a desktop font and you don't have the web version? Or, you have the web version but the license only includes usage on one URL?
Also, you'd still need to include the @font-face code manually for every font.

**Here's an example for a common font from my PC's font files:
Webfont (WOFF,EOT,TTF,SVG) $29.00 - if you purchase a license that covers 10,000 monthly pageviews, you will remain within your license as long as you do not get more than 10,000 views per month.
App $290.00 - Licenses are purchased based on the total number of installations of your app across all platforms, such as iOS, Android, and Windows Phone.
So, including it in the drop-down is useless, because everytime I want to use it, I have to purchase another instance of it and install the @font-face code on the site it will be used on. If I use it on 10 sites, it would be listed 10 times in the drop-down, once for each purchase/install.

I'm confused. What else is new? Lol.

In Paint I have some fonts I added to it and in Photoshop I added Greyhound. Can I add it to RSD?

I know you are explaining but I am not understanding

Thanks in advance..

Those programs are using desktop fonts from your fonts folder. If you use those fonts on a website project, you'll see them on your computer, but they won't show up for anyone else.
Web fonts are different. You can't install them to your system fonts folder.
If you installed Greyhound on your computer, then it's a desktop font - not a web font.
If you purchase the web version, you'll get a folder with all the files I mentioned above.
Sorry if this is confusing :-S

I have the web font for Greyhound.

How can I see it as a dropdown within RSD?

Thanks .

YOU CAN'T. The only fonts that will show in that list are standard web fonts* and Google web fonts.
There is no way to add custom (or desktop) fonts to that list.
Forget about it ever showing up in RSD's WEB FONTS list.

If your Greyhound file is a desktop font, you won't be able to use it for your website. If you did purchase the web version, you'll have to do what I showed you above to manually install it onto your site.

*http://www.cssfontstack.com/

Thanks for the clarification pb .

Maybe Coffee Cup can add the ability to import fonts in a future update .

I don't see how. As I mentioned above, there are way too many considerations involving licensing and usage.
Just learn how to use @font-face, it's not difficult once you go through it.