There are many different free programs that you can use to convert documents into PDF. One of the most popular programs is called 'Cute PDF Writer'
which can be downloaded by clicking here
Once you have downloaded and installed the software you can start to convert documents into PDF. To convert a document, first of all open the document to be converted in PDF and select the 'Print' option (see below).
You will now be shown the print properties window which will display all of the printers that you print to. You will see that one of the printers will be named 'Cute PDF Writer' (see below).
Select the 'Cute PDF Writer' printer from the choices and click on 'OK'. You will now be shown a window asking you to enter a name and also where the converted PDF will be saved (see below).
Once you have given the file a name and chosen where it will be saved click on 'OK'. the document will then be converted into PDF for you.