PDF files are optimized for the web by rendering text before graphic images and hypertext links. Ping is a basic network program that lets you verify that a particular network address exists and can accept requests. The verb ping means the act of using the ping utility or command. Ping is used diagnostically to ensure that a host computer you are trying to reach is actually operating. Ping can also be used with a host that is operating to see how long it takes to get a response back.
Ping operates by sending a packet to a designated address and waiting for a response.
The computer acronym was contrived to match the submariners' term for the sound of a returned sonar pulse. Telnet is the way you can access someone else's computer, assuming they have given you permission. The web or HTTP protocol and the FTP protocol allow you to request specific files from remote computers but not to actually be logged on as a user of that computer. With telnet, you log on as a regular user with whatever privileges you may have been granted to the specific applications and data on that computer. The result of this request would be an invitation to log on with a user ID and a prompt for a password.