You can use an eBook management software called Calibre (Internet download) to convert it from PDF to EPUB or .mobi, whichever your Kindle uses. Just google "calibre eBook management" and you'll find the download link. Do take the tour first, it makes life much easier.
You can then also use Calibre to send the book to your Kindle, I think. Plug your Kindle into your computer, and if it shows up in Calibre's menu bar as one if your devices, then you're good to go. Highlight the book you want, click "send to device" and presto.
Not tried it myself as I don't have a kindle, but have read up as looking to get one for DH and he reads lots of PDFs. If you email it to your @kindle.com address and put "convert" in the subject line, it should convert it automatically