Migrate SQL Server binary datadump to postgresql

I just got a very big dataset (+/-55GB) in a binary SQL Server format.

Is there an easy way to import this file into a Postgresql Server? I found some converter-programs, but they ‘only’ convert from server to server and not file to file or file to server.

I don’t have access to a SQL Server, so importing it and using this temporary as a source is not an option. Nor am I an expert in SQL Server programs…

I hope somebody here has a solution….