When you use a Facebook's gear icon (top-right corner), first option you should find there will be
Use Facebook as. If you're logged in to your personal profile, you'll see your Pages names there. If you like, share or comment anything on Facebook, it will be marked as your personl profile.
If you click any of Page name there, you switch to using Facebook as that account (page). From this moment, if you like, share or comment anything on Facebook, it will be marked as your Page, not your original (private profile).
You can switch there and back from and to your private profile as many times as you want.
Many things in Facebook are prohibited to be liked, commented or shared as Facebook Page. This includes private profiles at first. Actually you can like, share or comment only another Facebook Page if you're using Facebook as your own Facebook Page.
But, if I'm not mistaken, this limit does not belongs to your own page. You can like, share or comment anything on any of your Facebook Pages, not matter if you're using Facebook as Page or as private profile. I have a few pages on Facebook and many stuff on them is liked privately or "as page". There are even some items, that are liked (or commented) both by my private profile and "as page".