No you won`t lose the documents. When you have downloaded and installed go to tools, options and expand the Load/Save in the left hand pane. Select General and at the bottom are two boxes, The left one will say text document. Drop the right hand box and scroll up to Microsoft Word 97/2000/XP.
Similarly drop the left box to read spreadsheet and then change the right hand to Excel 97/2000/XP. Similarly for presentations.