I just bought a ps4 and I was wondering if I can borrow a friends ps4 game and play it on mine? If I play it on my console will it harm my friends psn account?
Yes, you can borrow your friend's PS4 game and play it without any problems or repercussions to either of your accounts.
Borrowing games from friends is essentially the same as buying games second-hand, which is still possible as of 2016-05-01, but only with disk-based games.
Note that you cannot redeem any DLC codes that your friend has already redeemed, as these can only be redeemed once.
You may not even need to borrow your friend's games in the first place, thanks to the PS4's new Share Play feature.
How to use Share Play.
Share Play has a couple of restrictions you might want to keep in mind:
Share Play allows unlimited 60 minute sessions.
A host may only invite one friend per session.
Shared games must be available on PlayStation®Store in both the host’s and friend’s countries for Share Play to be used.
German users can use Share Play only with other German Sony Entertainment Network account holders.
Games must be multiplayer.
Games using PlayStation®Camera not supported.
Any trophies earned by friends are not retained.
Hosts must have a PlayStation®Plus membership.
Friends must have a PlayStation®Plus membership to join a “play a game together” session.
PlayStation®4 system and Sony Entertainment Network account required.
Both host and friend must be PSN Friends and online at the same time.
If the Parental Control Level of the host’s game does not match the friend’s Parental Control Level setting, or if the friend’s age is lower than the game’s age rating on PlayStation®Store, Share Play cannot be used.
German friends are required to input their German ID number if the game is rated 16+.