copyrights for portrait photography

As a stock customer, you can use a photo and modify that and use that as you wish. There are limitations that you can do with the photo, but standard modifications should be OK.

All pictures depicting people come with a model release. You won't see that, but Adobe has seen that and checked it, so you are legally OK.

Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).

If you use an image of a real person you must obtain a signed model release from that person.