How do I get a field to be required once someone enters any data into a date field?

In my form I have a "Document Date" field, when someone enters any date in that field, I want the field "Upload file" to show and be required.
Here is the script I wrote for a similar one but the field Filling_State = to PA. I just want any date entered to trigger a similar action.

if (input.Filing_State == "Pennsylvania")
{
    show Date_Estimate_Filed;
    show Date_Estimate_Filled;
    show Estimated_Filing_Amount;
    show Proof_of_Payment_Due;
    show Proof_of_Payment_Filed;
}
else
{
    hide Date_Estimate_Filed;
    hide Date_Estimate_Filled;
    hide Estimated_Filing_Amount;
    hide Proof_of_Payment_Due;
    hide Proof_of_Payment_Filed;
}