Hi Sjoerd,
It is by design that when you open a .S01 file, any symbols found in that file that have Manufacturer, Model Number and description attributes that do not match any existing product in the librarues are created as UDPs; this comes from the introduction of Stardraw Design 7 back in 2012 and was requested by users to ensure that the custom data they had created in, for example, Stardraw Audio 2007 would be available to them in Stardraw Design 7 with the greatest possible ease and transparency.
It would be counterproductive to display a prompt because each drawing might contain hundreds of products and you don't want to see a prompt for every symbol contained in the S01 file.
If you do not want to import symbols from a .S01 file use
File | Import instead of
File | Open Project.
Now that the UDPs have been created you can remove them in the normal way i.e. rightclick on the product in the Product Browser and choose
Delete Product.I hope this is helpful
.