Adobe PDF files—short for portable document format files—are one of the most commonly used file types today. If you've ever downloaded a printable form or document from the Web, such as an IRS tax form, there's a good chance it was a PDF file. Whenever you see a file that ends with .pdf, that means it's a PDF file.
While exploring the Internet, you’ve probably encountered the terms downloading and uploading. Downloading means receiving data or a file from the Internet on your computer. Uploading means sending data or a file from your computer to somewhere on the Internet.