Can't open ebook

I bought a business ebook a while ago and it was working fine. when I tried to open it today it didn't open. It gave me this pop up, "Unable to open Business Management for the IB Diploma"

"The original document file is missing.

/Users/MyName/Documents/Digital Editions/Business Management for the IB Diploma.pdf"

Can anyone please help me get acces to my ebook???

Thanks.