KDP is for self-publishers. However, if you have trouble formatting your file so it looks good as an ebook (a pdf will look terrible, by the way), there are companies you can pay who will format it for you. You will still upload it to KDP yourself.
Unless you have a lot of images, putting a fixed-format book from PDF into e-book form usually results in a mess. Vastly generally, e-books are page-size independent and need to re-flow to fit the device on which they are read.
Also, if you have a fixed-format book, you limit your potential customer base to those folks who have a device on which your book can be read.
For e-books, it's much better to format for the medium specifically, and to then upload to KDP.
Download Amazon's free book, Building Your Book for Kindle . It has some age, so when it talks about uploading in "filtered html" format, ignore that. If you have docx file that is properly formatted, you should be able to upload that.