Hello @mike33
I’ll try to describe the process with an example. Assuming the get parameter is: my_param and the the DropDown field you want pre-populate is the fieldname1, in this case:
First, insert into the page the shortcode for the variable:
[CP_CALCULATED_FIELDS_VAR name="my_param" default_value=""]
Second, insert a javascript block in the page’s content to define the default value of the field:
<code style="display:none;"><script>
cpcff_default = { 1 : {} };
cpcff_default[1][ 'fieldname1' ] = my_param;
</script></code>
Finally, insert the form’s shortcode.
More information about the variables’ shortcodes, and how to define the default fields’ values, visiting the following links:
https://cff.dwbooster.com/documentation#javascript-variables
https://cff.dwbooster.com/documentation#populate-form
and that’s all.
Best regards.