Often you need to create a PDF file when sharing a document.
One application I have found particular useful in doing this is PDFCreator, which is a free, open-source software. You can create PDF files from documents, spreadsheets, presentations, emails, websites and virtually any file that can be printed. It works as a virtual printer so if you can print it, you can turn it into a PDF document.
To create a PDF file, when the software is installed, select to print the the document and select as a printer, PDFCreator.
Couldn't be any easier.
You can download the software here for free.