Questions about Flash Player

Hi there,

I fully understand Adobe no longer supports Flash Player anymore.
I have created some content by Flash, the ONLY I need that is installing Flash Player on PCs to play content in my own programs without using browsers.

But there is a couple queries as bwlow:

First, is it legal or not to install Flash player in a PC?

Second, without using any network connection, what kind of security issues should be concerned?

I am very appreciated for your reply.