I have iPad first generation, when I transferred books from ereader Sony store to kobo

I had to transfer my books from ereader Sony stoe to kobo books.  Transfer when but my books will not open.  Error states adobe digital rights mgmt, need to sign in.  I can't find adobe on my iPad first generation.  I am unable to find a download for version 5.5   What can I do to open my eBooks?