Yes, you can re-define the pre-loader file to your designed flash file.
Here are steps in detail:
Step1: Use Boxoft PDF to Flipbook to convert PDF to Flash Flipbook in HTML format;
Step2: Open output flipbook folder on your computer, then copy your Pre-loader file into this output folder;
Step3: Rename your per-loader file as “book.swf”
All is done, you will get your swf play before loading pages.
To test, just double click the html file (index.html for example), or upload all the files online and then test.
Here is our published pre-loader flash changed DemoBook