PDF Creator is an open source program that allows you to create PDF files from any program you can print from, such as Word, PowerPoint, etc.
Save it to your computer then double click the file to install it. There will be several options you can set during the installation but typically you can just accept the default answers for all of those options.
Once installed, it sets up a PDF Creator as a new printer on your machine. When you have a file you want to convert to a PDF document, just open the file, select Print from the File menu. Then select the PDF Creator as the printer. You will be prompted for a title for the document. Enter that and then click the Save button at the bottom. The next screen prompts you for a location to save the PDF file. Navigate to where you want the file saved and then click the save button. It will automatically open the new PDF file that you’ve created in Acrobat Reader.