I have created form commands for it and have created field for this on session. when i look at properties of Form Field in Form Editor, the 'Linked Form command' field is filled with form command. that is correct.
Aamir, check if your Session's DFE property is set to Rich View.
Refer to the screenshot, you have to create the new form command and set the command type to field and associate to a field to get the button.
Refer to field level help:
For all of the session's form tabs, the form command appears on the form's Specific menu, and/or as a button on the form.
The form command only appears on the session's Specific menu when a user selects the tab that includes the group you define in the Group/Field Number field.
The form command appears as a button on the form, behind the field whose Sequence Number you enter in the Group/Field Number field.
The form command appears as an option in the session's print menu.