Generating a PDF when a document is created in Firebase Cloud Firestore

I'm developing an app that creates a PDF based on a web form.

I am currently attempting to use pdfmake to generate the PDFs based on a firestore document create trigger

import * as functions from 'firebase-functions';
const admin = require('firebase-admin);
admin.initializeApp();
const PdfPrinter = require('pdfmake');
const fs = require('fs');

export const createPDF = functions.firestore
    .document('pdfs/{pdf}')
    .onCreate(async (snap, context) => {

        var pdfName  = context.params.pdf;
        var printer = new PdfPrinter();

        var docDefinition = {
        // Pdf Definitions
        };

        var options = {
        // Pdf Options
        };

        var pdfDoc = printer.createPdfKitDocument(docDefinition, options);
        pdfDoc.pipe(fs.createWriteStream('tempDoc.pdf'));
        await pdfDoc.end();


        // Upload to Firebase Storage
        const bucket = admin.storage().bucket('myproject.appspot.com');
        bucket.upload('tempDoc.pdf', {
            destination: pdfName + '.pdf',
        });

        return fs.unlinkSync('document.pdf');
    });

The trigger is called, however i get the error "Error: ENOENT: no such file or directory, stat 'document.pdf'"

I have tried it with the onCreate function being async and without.

Any help is greatly appreciated