If you are working with PDFs that contain very high resolution images and render slowly on screen, you can speed up rendering by adding alternate images and then clicking the PitStop Speed Up Image Display button (available in the Enfocus View Modes toolbar (Acrobat 8 and 9) or the PitStop View Panel (Acrobat X and XI)).
You can use this Action to add low resolution alternate images.
Select the preferred downsampling.
Bicubic looks best but is slowest; subsampling looks worst but is fastest.
Specify the preferred resolution.
72dpi is good for screen viewing.
Set Resample above to a higher value than the dpi chosen above.
PitStop suggests a value, but you can change it as required.
Select Convert to RGB for even faster on screen rendering, but in RGB color values.