This bucket policy from the Bucket Policy Examples documentation page shows how to Grant Read-Only Permission to an Anonymous User:

{
  "Version":"2012-10-17",
  "Statement":[
    {
      "Sid":"AddPerm",
      "Effect":"Allow",
      "Principal": "*",
      "Action":["s3:GetObject"],
      "Resource":["arn:aws:s3:::examplebucket/*"]
    }
  ]
}

They will be able to access files, but will not be able to list, delete or upload objects.

The permissions interface allows to to control this directly.

1. Open the root of the bucket in the management console. At the top, you should see several tabs. tabs interface
2. Click on the permissions tab. A set of four white buttons will appear.
3. Click on the 'Access Control List' button.
4. In the Public Access section, there will be a radio button with the word Everyone next to it. Click it. radio button
5. You get a dialog on the right. Make sure to uncheck the List Objects option. access to root list
6. Save and you're done.

If you try to look at your root, you should now see Access Denied Access denied

Just head over to the AWS S3 console and select the file. You can change this files permission so that it suits your needs.

You could try it the other way around as well. Disable public bucket access and only make the files you want to share public. This should work as well.