As a general rule of thumb, I use 1 cm margins when producing pdfs. I work in the geospatial industry and produce pdf maps that reference a specific geographic scale. Therefore, I do not have the option to 'fit document to printable area,' because this would make the reference scale inaccurate. You must also realize that when you fit to printable area, you are fitting your already existing margins inside the printer margins, so you end up with double margins. Make your margins the right size and your documents will print perfectly. Many modern printers can print with margins less than 3 mm, so 1 cm as a general rule should be sufficient. However, if it is a high profile job, get the specs of the printer you will be printing with and ensure that your margins are adequate. All you need is the brand and model number and you can find spec sheets through a google search.