Kindle book file to PDF for flash drive.

10 years ago now with the help of people per hour I published a Kindle book/manual . I would now like to supply it on branded flash/USB drives but the file format I have will not open on common everyday programs. (.mobi has been used).

I have reached out to the original freelancer but they are no longer contactable, however I do have all the original e-mails and attachments containing the formatted files and finished e-book. I also have all the original draughts in various formats if a total start from scratch is needed although I suspect the Kindle format can be relatively easily converted to a PDF or similar.

Basically what I'd like is for my e-book to be converted to a read only , secure format that can be installed on flash drives.

The kindle file size is 3 megabytes.