If you don't have ZBrush and you need to convert a polygroup to a single mesh, don't worry! We have you covered!
First, let's open Maya. Once in Maya, go to the top left corner and open the file.
Now let's go to import...
When you open the import option, first select the file that you want to import, you'll see on the bottom All Files as the type of file that's gonna be import.
Now let's change All Files to OBJ.
After changing to OBJ, you'll see a new option on the right, asking you if to import as a single object or as multiple objects.
Now when you hit import, it will open the file as only one mesh!
If you let the multiple objects, this is how it'll look:
Hope this little tutorial helps you! See on the next one!