Hopefully everyone has seen the videos covering the new drag-n-drop capabilities coming with Windchill 10.2_M020. If not, click on the video tab and look for the following videos. They do not have audio, but they give a clear understanding of how the drag-n-drop functionality is implemented.
What changes this in 10.2_M020, is a change to the default value of the Attachments preference named "File Upload Mechanism". It has always been set to "Use Java applet functionality to select and upload files" and now it will be set to "Use basic browser functionality to select and upload files". If the browser supports HTML5, the drag-n-drop functionality will work automatically.
If after upgrading your system to 10.2_M020, the drag-n-drop capability is not working, double check the value of this preference and ensure your browser supports HTML5. I have done all my validations with Chrome and Firefox but still need to test IE 10 since my machine is still on IE 9.
Can't wait for Windchill 10.2_M020? Try the built-in drag-n-drop features of Firefox and Chrome. I have noticed you can drag-n-drop files on almost any Browse, Upload or Add button in both Firefox and Chrome. Yeah, including Windchill. In fact, I dropped the included image on the Browse button in the community while creating this message.