Planning to integrate punbb into my site : a few questions

Hi !
I'm planning to integrate punbb into my website, as a comments system

each page of my site would allow visitors to post a comment to that page, and all the comments would be displayed ( and maybe paginated ) in the bottom of that page, just after the post form
( each page of my website would be bounded to a punbb topic )

i read the documentation, it says to use the common.php file, which gives access to all punbb variables and functions, but are All punbb functions/variables defined in the functions.php file ?

if you know if those functions exist, and where they are are defined  ( can't find the 1st in functions.php ) :
_ a function which gives me a list of all messages of a topic
_ a functions which gives all the information of a message ( the message body, the author etc ... )

If i'm right, when a page includes the common.php it can recognize the punbb user, then is it possible to post a message to punbb from outside it ? ( a ready to paste html form code for example, which of course recognizes logged users )

thanks in advance