How to transfer a pdf file to my kindle paperwhite?

Question

How to transfer a pdf file to my kindle paperwhite?

Answer 1

You first need one or more apps on your iPad that support the types of file that you want to copy over to it, the iPad doesn't have a file system link a 'normal' computer, everything has to be stored within an app.
For PDFs there are free apps such as Apple's iBooks app and also Adobe Reader - and paid-for apps such as GoodReader (which also supports read-only of word and excel documents). For documents the options include Apple's Pages app for Word documents, Numbers for Excel spreadsheets and Keynote for Powerpoint. And from third-parties apps such as Documents To Go ('premium' version) and QuickOffice Pro HD. As to how you then get the file to your chosen app will depend upon what the app supports - different apps will have different ways of copying their content to/from a computer e.g. via the file sharing section at the bottom of the device's apps tab when connected to iTunes, via your wifi network, email, dropbox etc.
For iBooks, which supports PDFs, you should be able to add the PDFs to your iTunes library via File > Add To Library, and they should go into the Books section of your library. You can then sync them to iBooks by connecting your iPad to your computer and selecting it on the left-hand side of your computer's iTunes (if you have iTunes on your computer then you can enable the left-hand sidebar via control-S), and on the right-hand side use the Books tab to select and sync them to the iBooks app.