Pasta vs. maleta
While both pasta and maleta relate to carrying items, their usage as "briefcase" depends heavily on the region and the rigidity of the bag. Generally, Portugal uses pasta as the standard term for a briefcase, while Brazil often reserves that word for folders, holding maleta for rigid, hard-shell cases.
Pasta
A2In Portugal, pasta is the universal word for a professional briefcase used to carry a laptop or documents. In Brazil, pasta typically refers strictly to a thin paper or plastic folder used to organize sheets of paper, or a soft, zipper-less portfolio bag.
O advogado português sempre leva a sua pasta para o tribunal.
(The Portuguese lawyer always takes his briefcase to the court.)
No Brasil, coloquei os documentos dentro de uma pasta de plástico.
(In Brazil, I put the documents inside a plastic folder.)
Ele comprou uma pasta de couro elegante para as reuniões em Lisboa.
(He bought an elegant leather briefcase for the meetings in Lisbon.)
O aluno guardou a tarefa na pasta escolar.
(The student put the homework in the school folder.)
Maleta
B1In Brazil, maleta is the common term for a rigid, box-shaped briefcase (often hard-shell) or a doctor's bag. In Portugal, maleta is rarely used for an office briefcase; instead, it usually refers to a small travel suitcase or a specialized kit case, such as for tools or makeup.
O executivo brasileiro carregava uma maleta preta rígida.
(The Brazilian executive was carrying a rigid black briefcase.)
Em Portugal, usei uma maleta pequena para levar minhas roupas de fim de semana.
(In Portugal, I used a small suitcase to take my weekend clothes.)
O médico abriu a sua maleta para pegar o estetoscópio.
(The doctor opened his bag (briefcase) to get the stethoscope.)
Ela guarda as ferramentas nesta maleta de metal.
(She keeps the tools in this metal case.)
Summary
To sound natural: use pasta for a briefcase in Portugal, but strictly for a document folder in Brazil. Use maleta for a hard-shell briefcase in Brazil, but primarily for small travel suitcases or tool kits in Portugal.