To allow public read access to your files in a S3 bucket, you can create a bucket policy that allows the s3:GetObject action on all files in the bucket. 
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "PublicReadGetObject",
      "Effect": "Allow",
      "Principal": "*",
      "Action": ["s3:GetObject"],
      "Resource": ["arn:aws:s3:::Bucket-Name/*"]
    }
  ]
}