PDF files cannot be used on most Kindles as the pages won’t get “text formatted” to fit into the screen. They will just appear with a very small font, every page within a Kindle page which will make reading almost impossible.
One of the best formats for Kindle is Mobi, you can convert pdf files (Adobe Reader) into mobi files using Calibre, a free software program.
Download Calibre from here, free. The software needs installation. Once it was installed, open it, add a book (select its path), select the book, click on “Convert book”, select the input format and the output format. On input, you should have “pdf” if the file is for Adobe Reader and on output format, “.mobi” (for Kindle).
Once you click on the “Ok” button, the book will start the conversion. It might take up to 10 minutes to convert a larga book.
Once the process has reached 100%, the book was converted. Go to “my documents” from Windows, there should be a folder called “Calibre Library”.
Browse the folder, you should see your new .mobi formatted e-book.
Copy it into your Kindle by using the USB cable, and you should be ready to read.