As shown in the home page of the Swedish Migration Board, the section about Schengen visas, every Swedish Embassy can have it's own requirements for certain documents etc. to be added to the application for a Schengen visa.
The Swedish Embassy in Tehran has the following requirements:
Important information about the Visa queueThe high season for the Swedish Embassy in Tehran is from the month of April up to the end of August. During this time many people line up outside the Embassy in order to file their applications. The most burdened months in this respect are the months of May and June. The Embassy strongly recommends applicants who wish to visit Sweden in May or June to apply for their visas at least two months in advance.
It is possible to apply for a Schengen visa up to three months before the planned date of entry.