H have used your form successfully at a recent expo but now I need to use the same form at the next expo

how do i create a totally separate list / pdf list of these new people who register for this next expo and subsequent expos 

Will it be OK to use another copy of the form instead? You can clone your form and have another copy of it.

User guide: How-to-clone-an-existing-form-from-your-account

You can then use the new copy of the form for the next expo.

Since this is another form, the submission report data will be for this form only.

So you can now generate report for all the actual new registrants (separately from the previous report)

User guide: How-to-Download-Form-Submissions-as-Excel-CSV-PDF

Hope this help. Let us know if you need further assistance.