I finished my M.Sc. dissertation a while back but I wrote it in Portuguese. I am applying for postdocs now and in some they ask for my research documents. Should I translate my Dissertation or is it wrong? And if yes, what notes and where should I write to identify it as a translation?
No, you don't need to translate the entire dissertation just for an application. That would be an unreasonable amount of work.
However, you should at least translate the abstract.
Better yet, write an extended abstract in English. This would be a 1-2 page summary of the contents of your thesis (brief background, methods, results, future work, etc).
Submit this together with the original Portuguese text of your thesis.
Commenters have suggested writing and submitting a paper (in English) based on your thesis. That might be a good idea in the long run, but it might not be practical to do before your applications are due. And you shouldn't rush the process if it would hurt the paper's quality. So I wouldn't focus on that as a solution to this particular situation.