In my application wokrflow I used Display form which doesn't allow me to Add file attachment during workflow approval process.
Now my requirement is Approver should be able to attach file during the workflow approval process and also Approver should not change form field except FIle attachment.
Any idea how we can do this?
What do you mean by you are not allowed to attach any files? When you open your form from your task, is the File Attachment control disabled? If so, check your form rules if that File Attachment control has been disabled. Normally your form should have a separate state that your workflow uses at specific step, so you can start from there to check if there is any rule that might be disabling it.