这句话中的那个“which”指代some documents,“on joint ventures”是“some documents ”的后置定语,即：”关于合资企业的一些文件“.
He shows us some docHe shows us some documents on joint ventures which have comfirmed decision to set up a joint venture with you.是含有定语从句的复合句,即：
He shows us 【some documents on joint ventures（先行词）】【which（关系代词）】 have comfirmed decision to set up a joint venture with you.
可以还原成：
He shows us some documents on joint ventures,and【these doucments】 have comfirmed decision to set up a joint venture with you.