SAP provides a conversion for SAPscript documents to SMARTforms.
This is basically a function module, called FB_MIGRATE_FORM. You can start this function module by hand (via SE37), or create a small ABAP which migrates all SAPscript forms automatically.
You can also do this one-by-one in transaction SMARTFORMS, under
Utilities -> Migrate SAPscript form.
You could also write a small batch program calling transaction SMARTFORMS and running the migration tool.