If you want to visit Poland for business purposes, then you will need to apply for a Poland business permit. The type of permit needed is determined by the length of stay: C type permits are for stays of less than 90 days, while D type permits are for stays of more than 90 days.
This permit is valid in all the European countries which are part of the Schengen agreement.
You can stay for a maximum period of 90 days in Poland or any other country in the Schengen region with the business permit.
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