Blurb offers a few different ebook conversion paths for your book files, depending on if you still have the InDesign file or not.
Option 1: Upload the design you created with Blurb's InDesign Plug-in
Upload your print or ebook designs as an ebook directly from the Blurb Book Creator plug-in for Adobe InDesign. This is the preferred workflow to honor your design and will give a more accurate conversion to ebook. (Note: ebook creation is not available with InDesign CS-3)
You can upload your print designs as an ebook with Blurb if you’ve created your print book with one of the Blurb InDesign Plug-ins or Blurb Templates. Follow the directions below to get your print templates into the Blurb Book Creator for upload as an ebook.
If you created your print design in the latest Blurb Book Creator, and it’s in your list of Books on the left-hand side of the plug-in, simply select the print book in the list, and in the bottom section set Book Type to ebook and upload. Quick and simple!
Option 2: Convert into ebooks from your uploaded PDFs
Blurb can convert your uploaded PDFs into an ebook by selecting "Convert this book to an ebook for the iPad" on your Book Detail page on Blurb.com. This option converts from a PDF file into an ebook, which is not the best workflow for quality of conversion. This option is mainly for non-InDesign users or those who no longer have their original InDesign files.