Mandatory drop downs and completions before signing/saving PDF

Hi All,

Hopefully someone can help, I've seen similar threads but nothing concrete. Please see picture below, essentially I need to, when selecting an option from the top drop down, make the corresponding fields become mandatory, After this the digital signiture cannot be added until both the top drop down and subsequent fields have been completed.....

I'm pretty sure this may be a javascript option but my knowlege of java is limited.

Any help would be greatly appreciated.

Thanks

Ben