If you use Adobe Distiller to create your PDF's then we recommend you use the following settings.
Select Adobe PDF from the list of printers
Select "Chose paper Source by PDF page size"
Click on the "Properties" button
Select "Smallest File Size" from the default settings
Click the Edit button
Click the "General" folder on the left
Select "Acrobat 4.0 (PDF 1.3)" from the Compatibility options.
Change the resolution to "150"
Select "Optimize for fast web view"
Click the "Images" folder on the left
Change the "pixels per inch" settings as highlighted in the image below.
Click the "Color" folder on the left
Under the "Color Management policies select the "Convert All Colors to sRGB" option
You will now be asked to enter a name for these settings. Enter a name that you will recognize next time such as "Flipbook". In future you will only need to select "Flipbook" in step 2 which will automatically load these settings.