FREE print driver (like many others) I don't know how others works, this one works well.
Set up a custom paper size for your kindle (IDK the sizes off hand they have been posted before, k3 is probably like 3x5 inches or something)
If you don't set a custom paper size, it will assume 8.5x11 which will be almost unreadable on K3, fine on DX
when you want to print something from web, highlight the part you want, for "print range" select "selection" rather than pages, select PDFcreator printer, and it will create a file.
If you have a word document, or something else, just print the whole document into a PDF container.
Oh in the print driver, you can also set up zooming, scale, and compression and whatnot, to get better results and make stuff more visible, but it also depends on what you are using to print with (like web browser or whatever, so set up paper size correctly)