In addition to what Andi said about above, is there a particular reason why you want to capture those details before the user clicks on Submit? Assuming the code passes the form filled data in the arguments of the submit call, you could always try capturing that if you have the flexibility.
As we need to know what user have feed in form, so want to know whether there is any functionality is there or not in DynaTrace.
Sometimes user says that they have filled with some details but after submitting the form it is showing something else. So we want to sure whether user have filled with correct details or not.
So - what you want to do is validate what type of data they entered. I think you have two options
#2: If you are talking about regular HTML Form Fields the Submit will take this data and will send an HTTP Request to your backend server. This is where the Dynatrace AppMon Agent (Web SErver, Java, .net, ...) can capture these form fields as HTTP Parameters. You can then see the form field values on the PurePath itself.
I think #2 is the best option. All you need to do is edit the Sensor Configuration for Web SErver, Servlet or ASP.NET (depending on your technology and installed agent) and instruct dynatrace to capture certain paramerters. I have several youtube tutorials that discuss how to configure these sensors:
* Basic Sensors: https://www.youtube.com/watch?v=f9XL4MDyLlc&list=P...
* Advanced Sensors: https://www.youtube.com/watch?v=lRtG7Js2cY4&list=P...