In order to reduce any risks the promissory note shall be drawn up in the form of a notarial deed. The difference is that if your friend will sign a promissory note in a private procedure or even if the notary public will simply certify his signature on the promissory note, then (if the debt won’t be returned in due time) the procedure of recovering the money through court may be complicated. In this case you will have to go through long court proceedings, including all court instances in accordance with general provisions (considering all possible judicial proceedings it may take up to 5 years).
However, if the promissory note will be drawn up in the form of a notarial deed, then the procedure for obtaining a relevant decision of the court (i.e. the procedure for undisputed compulsory execution of obligations) won’t take more than a month.