The book transferred to my kobo e-reader is unreadable

Hello everyone,

I'm facing an issue transferring an .epub book to my Kobo Clara e-reader :

1) I bought the book on a website, downloaded the .ascm file and added it to Adobe Digital Editions on my computer.

2) It's perfectly readable on ADE, but I need it on my e-reader.

3) I transfered it to my e-reader, which is connected with my Adobe Digital Editions ID.

4) When I used the e-reader, the book didn't even have a cover, the thumbnail was only a white page with the title of the book. When I try opening it, it's just a blank page and it's over, the book is marked "finished".

I used the exact same procedure for another book and it worked fine, so I don't understand why it isn't now. Do somebody know how to fix this issue ?

Best regards