If is a package then you can get the source for that with:
select text from all_source where name = 'PADCAMPAIGN'
and type = 'PACKAGE BODY'
order by line;
Oracle doesn't store the source for a sub-program separately, so you need to look through the package source for it.
Note: I've assumed you didn't use double-quotes when creating that package, but if you did , then use
select text from all_source where name = 'pAdCampaign'
and type = 'PACKAGE BODY'
order by line;