Can’t send pdf file from an input to my telegram bot through telegram-bot-api

My goal is to send a pdf file from an input to my telegram bot after the submit button has been clicked. According to the telegram bot api documentation (https://core.telegram.org/bots/api#sending-files), the way to achieve this is to upload a file using multipart/form-data.

Here is what I did:

document.querySelector('#sumbitButton').onclick = () => { // my submit button
  
    const input = document.querySelector('#file-input'); // my input
    const formData = new FormData();

    formData.append('pdf-file', input.files[0])

    fetch(`https://api.telegram.org/bot<my token>/sendDocument?chat_id=<my chat_id>`, {
        method: 'POST',
        body: formData
    }).then((success) => {
        console.log(success)
    }).catch((error) => {
        console.log(error)
    });

}

But I’m running into 400 error.