I do not practice in MD. However, you do not need a MD DL if you do not become a resident of Maryland. The rule is the same in many states. YOu have a 60 days grace period to apply for a MD DL. Please check the website of the MD DMV http://www.mva.maryland.gov/FAQ/
In addition, please check this information carefully because you have Partial Reciprocity between PR and MD for your DL. Check the PR Departamento de Transportacion y Obras Publicas. http://www.dtop.gov.pr/servicios/det_content.asp?cn_id=97
and the MD DMV
Of course this is the case in which you need to exchange your DL.
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