Nodejs Extra Data in FormData

I am sending a http request with a file to Sharepoint. Some file types, such as png or other images become corrupted and unreadable. When looking at those I see extra object data at the head e.g.

----------------------------826320949470377643449533
Content-Disposition: form-data; name="file"; filename="mypdf.pdf"
Content-Type: application/pdf

and at the bottom:

----------------------------826320949470377643449533--

Is there a way to prevent this? The code I am using looks like:

const contentType = mime.contentType(fileName);
const data = new FormData();
data.append('file',fs.createReadStream(path));
const fileSize = req.headers['content-length']
fs.promises.file(file)).size
const fileSizeLessByte = fileSize-1;
const contentRange = 'bytes 0-'+fileSizeLessByte+'/'+fileSize;
const contentLength = fileSize;

var config = {
    method: 'put',
    url: uploadUrl,
    headers: { 
      'Content-Range': contentRange,
      'Content-Length': contentLength,
      'Content-Type': 'multipart/form-data'
    },
    data : data
  };

Answer

I was eventually able to get this working by using readFileSync instead of FormData and not using the multipart content type as O. Jones suggested:

 const contentType = mime.contentType(fileName);
 const fileStream = fs.readFileSync(path);
 const fileSize = Buffer.byteLength(fileStream);
 const fileSizeLessByte = fileSize-1
 const contentRange = 'bytes 0-'+fileSizeLessByte+'/'+fileSize;
 const contentLength = fileSize;

 const config = {
     method: 'put',
     url: uploadUrl,
     headers: { 
         'Content-Type': contentType,
         'Content-Range': contentRange,
         'Content-Length': contentLength
     },
     data: fileStream
    };