I have a requirement to read Excel data stored on Office 365 and populate in Nintex Form Controls, can this be achieved in Office 365?
Also, Is it possible to attach a Excel File Template automatically to Nintex Form based on a drop down change.
You cannot In O365 you have no access to "Excel Services" as you could have in on premise (but only if you have SharePoint and Nintex both in Enterprise version).
So unless your Excel file is not a plain CSV file (so you could simply read its contents as a text), then no OOTB option is available.
Retrieving data ...