Hi Andy, fonts are better supported by the app in DWG/DXF vector formats. This way it’s imported as a drawing that can be edited in the app and from which you can generate 3D bodies.
The app supports PNG format import but this will be imported as an image and 3d bodies can not be generated from images, only from drawings.
You also can import nicely designed letters as an image and the use the image as an outline to trace the sketch in the app if this is the case.
I will suggest you create the letter using Illustrator or Autocad and then import it into the app in DWG/DXF format.
Also here’s a drawing workspace of all letters created by an amazing user that can be downloaded and imported into the app: