Migraciones has copies of the "precontrato de trabajo". Technically you need to present this (completed, signed and certified by an escribano) to migraciones along with all of the other paperwork prior to beginning actual work at the company. However, of course, many don't, and have already started working, and technically you are working "en negro". When migraciones accepts your file for processing, they issue you a "precaria" which is a 30 day work permit. With that document your employer can register you with AFIP as being employed. When you go back to migraciones after the 30 day processing period, you must bring the "alta temprana" with you. This is a form that your employer prints out from the AFIP website, to demonstrate that you have been enrolled with AFIP for tax purposes by your employer. In between these 2 steps, preferrably immediately after receiving your "precaria" you must go to ANSES to get your "CUIL" (Código Único de Identificación Laboral - this is the equivalent of a social security number) because your employer WILL NEED the CUIL number to enroll you with AFIP. I did this personally 7 years ago, however I have accompanied several people over the years to migraciones, 2012 being the last time I did this. The process hasn't changed. What has changed (and for the better) is the DNI process, it's VERY modern and efficient, and fast. When I got my first DNI in 2008 it was like being in the dark ages....the little red book, with the people stamping and signing pages, waiting in endless lines, impossible to call or e-mail for info. Good luck.