This computer is not authorized to open this e-book because this item is linked to a vendor ID

I have a ebook in pdf format which has been previously downloaded on my computer (PC). When I try to open it in Adobe Digital Editions it says authorization needed, with the following messages:

This computer is not authorized to open Clinical_Exercise_Physiology.pdf because this item is linked to a vendor ID

To authorise your computer to open this item, enter your login ID and password associated with this item and click authorise.

The issue is that I don't remember the login details linked to this item as the e-book was purchased over two years ago. Is it possible to remove the vendor ID or find the login details linked to this book.