How can I load an ebook from my computer to my Kobo Clara device ?

Hello,

I have some epub ebooks on my computer. I would like to load those books on my Kobo Clara device.

I tried ADE,firstly with the last version 4.1, but my Kobo Reader told me that I am not authorized to open the book. I see it but nothing happens. On the forum someone told that it would be easier with the 

3.0. I have tried with this version, it is still the same. I see my book in black but cannot open it.

Other persons seem to have the same problem, but nobody from Adobe is able to help us to solve the problem. 

I did not find how to authorize my Kobo Reader versus ADE. Is there somewher a link to do that ?

Please help if possible because now I need to get mybooks. 

Many Thanks

Marie