langchain/document_loaders/pdf.py/MathpixPDFLoader/clean_pdf
class MathpixPDFLoader:    def clean_pdf(self, contents: str) -> str:
        contents = "\n".join(
            [line for line in contents.split("\n") if not line.startswith("![]")]
        )
        # replace \section{Title} with # Title
        contents = contents.replace("\\section{", "# ").replace("}", "")
        # replace the "\" slash that Mathpix adds to escape $, %, (, etc.
        contents = (
            contents.replace(r"\$", "$")
            .replace(r"\%", "%")
            .replace(r"\(", "(")
            .replace(r"\)", ")")
        )
        return contents