There are editors around for Gerber files, but it's quite specialized software. PCB manufacturers use it for example for panelization.
Your TTF text is also not really TTF. The PCB software has converted the text to separate vectors, and put those vectors in the gerber files. (It is probably possible to generate D-codes or macro's for each letter to create a "font" like think in a gerber file, but I don't know if such a thing is really done).
It may be possible to create a simple PCB project, create gerbers from it, and then hand-copy a part of the content from one gerber file to another to add some text, but it will need experimentation and it's error prone.
In KiCad it is quite easy to back import a set of Gerber files to create a PCB file.
The result is not perfect, for example it does not have real footprints, because those don't exist in Gerber files. But the result is usable. If you want to go further, it is easy (but it takes some time) to remove the constructs that are supposed to represent the pads / footprints, and put real footprints on the PCB.