langchain/document_loaders/pdf.py/MathpixPDFLoader/send_pdf
class MathpixPDFLoader:    def send_pdf(self) -> str:
        with open(self.file_path, "rb") as f:
            files = {"file": f}
            response = requests.post(
                self.url, headers=self.headers, files=files, data=self.data
            )
        response_data = response.json()
        if "pdf_id" in response_data:
            pdf_id = response_data["pdf_id"]
            return pdf_id
        else:
            raise ValueError("Unable to send PDF to Mathpix.")