How can I transfer an Amazon ebook downloaded to my pc to a non-kindle device?

I bought a couple of ebook collections from Amazon which I want to transfer to my husband's Wolder MiBuk 7. I downloaded the books to my PC as I did not want them on my Kindle but have not found a way of transferring them. The mobi file format will be acceptable to the MiBuk so that should not be a problem. I cannot believe that nobody has resolved this yet as there are now many alternatives to Kindles about.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia��).