XML files can hold any kind of data. If a software like QGIS should be able to read it, the software (or the developer) needs to know the XML schema of the data.
QGIS is able to read Openstreetmap XML data, and (with the LandXML plugin) data provided by Land Information New Zealand.
If you need support for other XML sources, you might have to do it on your own, or pay a developer to do it for you.
Currently, there seems to be no effort for supporting Adobe XML files in QGIS or GDAL.
The PDF file you linked in the comment can be opened in QGIS and GDAL as a raster file, but not as a vector file. You may extract the map data with
but that has only a poor resolution.
You can use https://superuser.com/questions/302045/how-to-extract-vectors-from-a-pdf-file, and save from inkscape to DXF format. That way you get the geometry into QGIS, but you have to georeference the data yourself using the countries borders.