For the submission of your application you need at least two letters of recommendation. The first one has to be an academic letter of recommendation from your university. The second one should be a professional letter of recommendation from your employer. If you prefer, you are free to upload more than these two mandatory recommendation letters. All letters have to be written individually by your referees with an official letter head, they should be hand signed and stamped by them (with an official office stamp) and must be of recent date.