It may be that Moon+ Pro can't work on the Libre Touch without rooting, however, I'd just keep trying earlier versions of the apk in the hopes one takes.
There seems to be a link to Moon+ Reader Pro v1.2.21 here:
http://mobileplanet-waryam.blogspot....-apk-1221.html
Once again, typical disclaimers since I've no way of testing this. Hope this helps.