Yes, the Default- .prt configuration files specify only a very small number of fonts, so that's all you see in Design when using those configuration files.
You must add more font references to your chosen configuration file (.prt). Of course, if you are using a Default- .prtfile, you can't alter those. You must make a copy, using a name that doesn't start with Default- , and then add fonts to that .prt, using Configuration Editor. In Design you would then use Format-Form Properties and select your new configuration file.
You do that only once. It's best to get your site's configuration file(s) in order and use your site's configuration files, not the Default- ones.
In Configuration Editor (just double-click the .prt file of interest), it is simply a matter of clicking on checkboxes beside the names of any fonts you want included.
In Design, you'll see all those fonts show up.
How awkward is this! Not at all. It's left this way (as opposed to some 'add font' gesture in Design), for your benefit. You want to establish some site standards as to which fonts to use. And you want to keep that list small. Not recommended that you go clicking every available font's checkbox.
Set up your configuration files!
The configuration file supplies only references to the fonts that you want to have available. If you want to have those fonts actually be available (and surely you do) then you must deploy them to those systems where you intend to run DocOrigin and make use of the fonts as specified in your configuration file(s).
STEP ONE: Ensure that you are legally able to copy those font files to those other systems! Fonts are often copyrighted. Fonts are worth money. Do not presume that you can copy any font to any other system. Obtain the legal rights to do so.
If your target system is a Windows system then one does the usual right-click on the TTF file and chooses the install font operation. It will end up under \Windows\Fonts.
On unix systems, there is no specific system folder to put them in. For DocOrigin use, you should copy the TTF file(s) into your .../User/Config folder. That is, right beside where you would deploy your .prt file.
Configuration files have the following line in them:
<TTFPath>$C;C:/Windows/Fonts</TTFPath>
Well, you might override that, but I bet you haven't (no need). It tells DocOrigin where to look for TTF (font) files. The first place to look is in $C, which is .../User/Config. If it can't find the referenced TTF file there it will look in the next place (if it exists on the system in question).