Apart from exporting an asset status report, you can determine if the PDF ebook exists by visiting the product page. The associated product formats are listed at the bottom of that page. A check ✓ in the Ebook? column indicate that the file exists. In the image below, we can conclude that the PDF ebook, the ePub ebook and the Kindle ebook exist.
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You can further determine if a product format has been distributed to wholesalers by visiting the product format page, then clicking the Distributions link in the right sidebar.