I am uploading PDF's to AmazonS3 manually, using Panic Transmis and via a PHP script/API. For some reason, some display in your browser, and some force download. I have checked permission and can not seem to see any issues, Can anyone help explain how to make PDF's always display in browser ( unless the user specifies otherwise ).
I don't think it is as browser issue.
You need to change the Content-Type and Content-Disposition.
Using the AWS S3 console, find the file and using the context menu (right click) select Properties then it's under Metadata.
Or change this programmatically: http://docs.aws.amazon.com/AWSSDKforPHP/latest/index.html#m=AmazonS3/create_object
In companion with well's answer, here an example: