title: How to get return from AWS-Lambda (event-S3-invocation type)?
body: <p>I have lambda that triggered by S3 event (uploading pdf-file to bucket).
  This lambda read uploaded pdf-file and produce new refactored pdf-file, put it to another bucket, and have to return presigned S3 URL (link) to that file for using at frontend.</p>
  <p>I upload first file to S3 bucket through API Gateway, so I get on frontend response only from POST to API, not from lambda.
  I can't figure out how I can return presigned S3 URL (link) from lambda to frontend.</p>