Hi naisa13,
I don't think there is anyway you can connect to Mongo DB from PAM. However, you can create a connector to get it working.
I can share a beta version of new PAM SDK using which you can create a Mongo DB connector and use it in PAM. It is very simple and easy to create.
Let me know if you are interested in that.
You can even refer to my blog post on PAM 4.3 features Announcement : PAM 4.3 Alpha build is published
Thanks,
Vinay.