All scsanned pdfs are going to be an issue with pure ereaders. the pages are just very large/memory intensive and so take a good deal of processor power to buffer and display. The libre pro is a five inch device i believe and so its going to be difficult to display them properly and with any sort of speed.
there may be a way to reformat them to fit more easily on that display and sort of optimize them for the processing power of the Libre pro but I am not that familiar with the various pdf software but there do seem to be some very knowledgeable people here on the Mobileread discussing pdfs in the Onyx/Ectaco/Pocketbook threads that may have an idea .
One thing you might consider is this bit of news i've just run across
http://www.the-digital-reader.com/20...30/#more-30725 if you have a "staples" there in the Miami area...