Yes, this can be done and there's no problem in doing it. Matter of fact, groups and pages are used as "Topics" when it comes to this, along with other pages and topics.
Lets suppose I have a pet shop and I want to target people who have interests for pets, I could target - pets, cat, dog, pet community, pet page. In this context, pet community and pet page become a Topic, and can be added as a target-public, targeting the people who liked this topic (meaning page or community) as a potential public.
I could even add - Google, Facebook or any other page or company as a target-public if I feel it's in context.
This is also one of the reasons why, when you create a page, you have the option to chose in what section will your page fit, whether it's in - sports, movies, comedy, entertainment, technology etc..., to fit in Topics, which will be used later in this concepts, and of course to have more chances to be found in an accurately search, among other things.
You'll want to access it through the Graph API. The details on pulling friends are here.
You can also play around a bit with the explorer tool to get a feel for things. In this case, you'd just append YOURUSERID/friends in the explorer window and request the information with a token.
If you're a masochist, https://www.facebook.com/YOURUSERNAME/friends?ft_ref=flsa will get you a list of all your FB friends. You can scroll until nothing more loads and then parse out the ID using XPath or one of the browser scraping tools. The stuff is in there but it'd be a real pain to get out.
Best Answer
A
Page User IDis a name for a page a custom Username for my Page or profile. It is visible to the public.An
App User IDis a code for a particular browser to protect FB users’ anonymity but to allow advertisers to target specific audiences. Details.