Many machines come loaded with Adobe Reader for reading PDF files. If yours didn't, you probably downloaded the free app the first time you stumbled on a PDF while surfing the Web. But you can also create PDFs free of charge.

Go2PDF: Go2PDF, like most third-party PDF creators, is a printer driver. You open, say, a Microsoft Word document, select Print, and choose Go2PDF as the printer. "Printing" converts the document to a PDF file. You can embed metadata within the file, including a title, subject, author name, and keywords for searching, and encrypt it with password protection. The catch: A tag on each page of your new PDF advertises the product and links back to the company Web site, where you can purchase a no-tag version.

PDFCreator: Don't want your PDFs marked with unsightly ads? Try the open-source PDFCreator. It's a printer driver too, but with a beefed-up interface: You can also create PDFs by dragging a document onto a freestanding PDFCreator window. PDFCreator lacks encryption and password protection, and it wasn't completely stable during testing. It also has one significant bug: If you create a PDF and give it the same name as an existing file, it will overwrite the existing file without even asking.

Pdf995: A barebones printer driver, Pdf995 won't add metadata, passwords, or encryption—but it doesn't slap ad tags on your documents, either. It does, however, launch a partner pop-up ad each time you create a PDF, unless you buy a sister version for, you guessed it, $9.95.