Full disclosure: right now FATpick will import gp3, gp4 and gp5 files. The "import song" button both enforces and mentions this, as does the user manual IIRC, but it's not something that's called out in any way.
If you have a gpx file (produced by Guitar Pro 6 or 7) then you'll need to convert it to gp5 to import into FATpick, at least for now. If you're using the GuitarPro app itself you can just save it that way. If you don't have the GuitarPro app TuxGuitar is free and handles this well (it works for editing GuitarPro files too).
Obviously it would be better to support .gpx directly, and for that matter things like MusicXML, too. But the GuitarPro format has to be more or less reverse-engineered, and gpx is unlike gp3, gp4 and gp5. Most files in the wild seem to be gp5 (or after that, gp3) anyway so that's where its at right now.
It seems like one could probably use some headless form of TuxGuitar on the back-end to convert gpx to gp5, but other than a cursory scan to see if that's a feature they already provide (it isn't) I haven't dug into it much more deeply than that.
Not the original poster, but absolutely. "Import custom tabs" is pretty vague in my eyes, and reading it just makes me think that the tool simply has a way to work with your own custom tabs. Just from reading it, I would've never guessed that it supports Guitar Pro tab import.
