CutePDF is what I regularly use at work and so far haven't had any issue with it. It's freeware for home and commercial use and doesn't contain adware or watermarks unlike some of the other so called "free" PDF makers. When installed, it appears like a printer.
The resulting PDF size depends a lot on the source document and the resolution you choose to print to the PDF printer at. Generally a good quality full A4 flyer with graphics will result in a 1MB to 2MB size PDF. If the document only contains text, the resulting PDF can be very small, e.g. several pages in a 100KB PDF.