Another interesting observation (don't know if it's relevant or not, but I'll just throw it in).
In C:\Program Files\Xara\Xara Designer Pro X\19\Filters\ENG\PDFImport\ there is an executable called pdf2xar.exe
Using pdf2xar.exe in command prompt, I was able to convert a basic PDF to a XAR file just fine. You just have to read the instructions and the rest is easy (Usage: pdf2xar input.pdf output.xar [options]). The output XAR file was valid.