1.It’s a Pleasure或 It's my pleasure与You are welcome.等习语意义相同,用来回答Thank you.即“不用谢”.
2.With pleasure与All right,No problem.I’d like to等习语意义相同.用于别人求你做某事,你很乐意去做的时候.
简单讲,It’s a pleasure用于事情发生之后,而with pleasure用于事情发生之前.
至于你所说的with my pleasure,根本没有这种用法,我想你说的是my pleasure
My pleasure是相当正式的说法,意思是“我的荣幸之至”.