There are salary restrictions for visit visa also.I think it is around 8000 QAR.As mentioned all the above documents are needed even birth certificate attested.Along with your engineering degree certificate,attested & translated to Arabic, consolidated marklists.You need to have NOC from company also along with 6 months bank statements showing only your salary credited.If your company is providing you with family accomodation,get some proof for it .so you can avoid rental agreement.

Best wishes.