[Frank Cox]

It might just be that individual pdf file.  Internally, pdf files are quite a mess since they can include all kinds of graphics, fonts, vectors and ghawd-knows-what as elements in almost any order.  They're almost (but maybe not quite) as much of a technical mess as Microsoft Docx files -- those contain everything up to and including raw memory dumps from your computer.

Having said that, you might want to try rebuilding that pdf.  If it's an internal hodge-podge of random elements, you could convert each page to a single image and make those images into a PDF file where there is just one simple image per page.  If you name it the same as the original pdf file on your tablet, then it would just be a drop-in replacement for what you have now and (as far as I know) all of your annotations should remain intact just as they are now.

There are several ways to go about doing this.  One of the easiest ways (especially for something with lots of pages) is to use imagemagick to convert the pdf to individual images (like a series of png files), then use imagemagick again to combine those images back into a pdf file.  At this stage you can also vary the density and size of the image of each page to optimize it for maximum readability on your screen if you like, balanced with maximizing the performance, of course.

After doing that (which may or may not take some experimentation depending on what your expectations are and how much time you want to put into optimization), you can compress the resulting pdf file and give it a more streamlined internal structure, which should also speed it up some when you're reading it on the screen.  Ghostscript will do that for you; here is a short script that I use for exactly this purpose:

#!/bin/bash
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile="${1%/}".screen.pdf "${1%/}"
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile="${1%/}".ebook.pdf "${1%/}"


This will give you two different output pdf files, named something.screen.pdf and something.ebook.pdf respectively.  The .screen file will (usually) be smaller than the .ebook file but it will (sometimes) be of a poorer output quality, so you'll want to view both of the output files and decide which one you want to keep after doing the compression.

After doing this, you will hopefully have a pdf file that will render faster and that should rev up the page turning and other pdf reading functions to at least some degree.