File System can be used in firebase cloud functions in my case

Question

I created a pdf to zpl converter for a recent local project, everything works perfectly,but the project to host it use firebase functions to deploy.

-Project Structure-

• index.js(file)
• controller(directory)=> convertorController.js
• routes(directory)=> converterRoutes.js
• processFile(directory where locally I save temporally files)

index.js

const functions = require("firebase-functions");
const express = require('express')
const app = express();

const port = 8080;


//Api Route
const convertorRoutes = require('./routes/convertorRoutes');
app.use('/convert-pdf-to-zpl',convertorRoutes);

........

exports.zlp_ip = functions.https.onRequest(app)

routes/converterRoutes.js

const express = require('express');
const convertorController = require('../controller/convertorController');

const router = express.Router();

router.route('/:width/:height').post(
   convertorController.conversion1,
   convertorController.conversion2,
   convertorController.conversion3
)

 module.exports = router;

controller/convertorController.js

//Native Node Js Module
const https = require('https'); 
const fs = require('fs');
 .................

const resizeImg = require('resize-img');



 //Create PDF 
 exports.conversion1=(req,res,next)=>{
try {
    if(fs.existsSync(pdfPath)){
       return next()
    }else{
        //Get Global Url
        let urlPdf = req.body.url_pdf;
        //Save pdf locally 
        https.get(urlPdf, function(response) {
            //Save file loccly 
            const file = fs.createWriteStream("./processFile/file.pdf");
            response.pipe(file);
            //If is onfinish start png conversion
            file.on('finish',function(){
                file.close();
                return next()
            })
        
        });
    }
} catch(err) {
    res.status(403).json({
        status:'failed to extract pdf',
        messahe:err
    })
}
}   

The other functions convert pdf to base64 and then to the desired format all temporary files being saved in processFile,when I uploaded the project to firebase and tested it, it gave me the following error in the postman << Error: could not handle the request/500Internal Server Error>>,after searching the internet I discovered that cloud functions work differently, they have a / tmp default.

I found an adaptation using .

const os = require('os');
let tmpDir = os.tmpdir();

and then I replaced the code path with my files

const pathPdf = tmpDir+'/file.pdf'
const file = fs.createWriteStream(tmpDir+"/file.pdf");

the first function is running, the file is saved without any problems, but when I try to access it in the next one to convert to png, it can't find it anymore. In total I have to save 3 files that I delete when the conversions are completed, but I can't understand how this cloud functions storage works.