system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How did the PDF format become so popular?
gpt
First, there was a need for a way to represent paper online. A PDF is a decent approximation of a paper document as it will print to actual paper without any issues. The PDF is an early example of "What You See Is What You Get", or WYSIWYG. This became handy when people would need to send print documents over electronically, as it could be reasonably assumed that the receiver could print it if they could open it.

Second, Adobe made its reader free. This meant that anyone could read a PDF across different operating systems. So, if you had to create an electronic document that was to be printed, you could safely assume that people would be able to open it via PDF.