The only way I know how to report on activities taken by a specific lead is to create a smart list. Try creating a smart list with the "Filled out form" filter, choose the date range, and export. I hope that helps!
Do you have the activity of Form Fill Out log as a SFDC completed task? If so you could run a report on activity subject contains "Filled out ABC Form."
Otherwise I think the only other way you'll be able to pull this report is through Marketo with a Smart List - filtering leads who filled out the specified form.