Can I create a form in which one has to register then the data he filled remains saved?

Would you like to save data to be shown when user opens the form again? 

If so, there is an option to enable form autofill: How-to-Enable-Auto-Fill-on-Forms

Alternatively, you can set up Save and Continue on your forms following this guide: How-to-Save-Forms-and-Continue-Later

Hope this helps! But, please get back to us if you need further assistance.