what is the format of invitation? Is email invitation acceptable?

Tariq, usually the duration of stay should be 30 days. However, some people acquired 60 days duration of stay. You should understand that duration of stay is decided by consular officer. By the way, Pakistanis can't apply individual L types. They should apply for Group L types by joining tours arranged by qualified agencies.

The invitation letter should be printed out if he sends you via Email. There is no exact format. However, you should include the following information:
1. applicant's information: name, sex and date of birth
2. applicant's itinerary: when to arrive and when to leave, where to visit
3. inviter's information: name, tel, address and signature