You won't be able to specify a unique link in the send email add choice option. But if the whitepaper link is the ONLY link in the email, I would do the following:
Trigger -
Fills out form w/ constraint added for specific page (in case the same form is used for other campaigns)
Flow -
1. Send email 1
2. Wait 5 days
3. Send email 2 w/ add choice:
a) Add choice is If "Not Clicked Link in Email" w/ email 1 selected in the drop down
b) default choice is do nothing
The above won't work if there are multiple links in the email, since it is simply looking for any link to be clicked. If you have multiple links in the email, let us know and we can suggest an alternative that will work in such a scenario.
Thanks,
Mike