Docx Document Serverless S3 Error while Putobject

I am stuck in a situation for a long time. I am trying to upload a docx file to S3 bucket , using Serverless framework

I was successful in uploading the docx document to S3 bucket.But what happened is, when I opened the document from S3. The document contained a buffer data converted to base64 string. i.e the big string about 23 pages.

The docx was corrupted.

MY Code

exports.putFile = async(event) =>{
  try {
    var bitmap = fs.readFileSync('./test.docx');
    let bufferValue = new Buffer(bitmap).toString('base64');
    const valueFromBucket = await S3.putObject(
        { Body: bufferValue, 
          Bucket: '********', 
          Key: '*****.docx',
          ContentType: 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
          ContentDisposition: 'attachment',
          ContentEncoding: 'base64'
          }).promise();
    return{
      statusCode: 200,
      body: JSON.stringify(valueFromBucket)
    }
  }catch(err){
    return {
      statusCode: err.statusCode || 400,
      body: err.message || JSON.stringify(err.message)
    }
  }
}

Serverless.yml

service: node11

custom:
  bucket: ******

provider:
  name: aws
  runtime: provided # set to provided
  stage: dev
  region: *****
  iamRoleStatements:
    - Effect: Allow
      Action:
        - s3:*
        - ses:SendEmail
        - ses:SendRawEmail
      Resource: "*"

functions:
  hello:
    handler: handler.*****
    memorySize: 1024
    events:
      - http:
          path: /
          method: get
    layers: # add layer
      - arn:aws:lambda:us-east-1:553035198032:layer:nodejs11:3
  putFile:
    handler: handler.*****
    description: put Object using S3 service.
    memorySize: 1024
    timeout: 5
    events:
      - http:
          path: putfile
          method: post
          integration: lambda
          cors: true
    layers: # add layer
      - arn:aws:lambda:us-east-1:553035198032:layer:nodejs11:3

I think the code is almost working , but this issue of the base 64 string which is contained in the uploaded document is the issue.

Any kind of help appreciated, Thanks in advance

It should not be necessary to convert the binary buffer to string before uploading. Drop the .toString('base64'), everything else ought to work.