You will need either Microsoft Word 2007 or Open Office which is free to use.

Word 2007

If you have Word 2007 you can install an add-on which will allow you to save your documents as PDF documents. Simply open the Help for Word, type in "Install and use the Save as PDF or XPS add-in from Microsoft", and follow the instructions. After you've done this, you'll have the option File>Save As>PDF

Open Office

Open Office is free, (open source) software which you can download here: http://download.openoffice.org. Open Office has the same components as Microsoft Office, ie it has a word processor, spreadsheets, presentation slides, etc. The equivallent of Word is Open Office Writer. As soon as you create a new document or open an existing document with Writer, you will have a menu option called File>Export as PDF which saves your document in PDF form.

No Spaces!

Don't forget that filenames for your website should NEVER contain spaces. If you have spaces in filesnames you will have problems viewing your documents. You can use dashes instead, eg standing-order-form.pdf instead of standing order form.pdf