Researches, term papers and any other documents after they were finalized are better to be saved in PDF to preserve their format. Documents in PDF files can not be altered and hence, you are assured that the document you send to anybody or about to be printed will remain the same.
When you are using Open Officentu, its word processor has a built-in PDF converter wherein you can automatically save the document you just made as PDF file. But now, I just found a free PDF converter that you can download and install on your Windows based computer. The free software is called doPDF5.0 PDF converter that can be installed as a virtual printer driver.
To convert your files into PDF files, all you have to do is to print your documents to the doPDF converter. Choosing the print option will allow you to save your current document into PDF file. The converted PDF file can now be open and viewed using the default PDF viewer. And since the doPDF converter is installed as a printer, you can convert any kind of document whether it is in Excel, PowerPoint, WordPad or NotePad.