In your web screens you can upload a file by allowing the end user to browse the local file system. This behavior is implemented by the Upload widget.
To allow end-users to upload files, in your web screen or web block:
Add the Upload widget. The end-user uses the 'Browser...' to choose the file to be uploaded;
Add a Button or a Link. When the end-user clicks on it, the file is sent to server along with the other inputs;
Specify the Screen Action that runs when the button/link is pressed. This allows you to manipulate the file content after the end-user uploads it to the server.
If your button or link has the 'Method' property set to 'Ajax Submit', a warning message is displayed, and at runtime the file is not uploaded to the server. To fix this, simply change the button method to 'Submit'.
Layout of Widgets | Upload Widget Properties | Upload Widget Runtime Properties | Apply Web Styles