That's the etymological fallacy. The name itself doesn't determine the meaning. According to that logic, python isn't a programming language either but a snake
The name in this case is defined by the meaning if you will. Programming languages are used to write programs. A HTML file is much closer to a PDF than to what can be considered a program.
Also fun fact python is named after the comedy group Monty Python rather than the snake.
Actually, PDF is a turing complete programming language.
PDF is a simplification and wrapper around the computer language PostScript - a PostScript or PDF doc literally runs on the printer or computer and outputs the rasterisation of the thing you want to print.
PostScript is language based around a stack. You can define functions (which may be fully recursive) that run on the stack.