Difference between .php .html .jsp .net etc?

Might be a stupid question but once the browser engine reads these files - they all get turned into just html elements yes? If not what kind of discrepancies are there between them? I understand there are issues between browsers due to the different rendering engines. But I'm only interested in the raw file output - not the engines. I'm trying to capture the DOM as a JSON and wondering if there might be issues depending on the language used to create the webpage.