Write a template script

I need to write a template script, something like the one built into the DLE, but I need specific tags and processing. The script should accept only one parameter - a link to a file or text, and as a result, process the file and text according to the built-in functions and give the result in the form of text. In total, about 30 template inserts will need to be provided. For those with little experience in web development, please do not bother.