In the year I have been reading this forum the subject form has never been discussed. As my Brasilian wife and I (an RNE holder) have just completed the process, I thought you'd like to know about it.
If you are a Brasilian who has been absent from the country for more than one year, and has CLOSED their CPF account with the RF (which you are required to do).....or you are a foreigner entering Brasil to live there, this document is for you.
In Canada for example, you register and upload numerous notarized documents on the consulate website as well as pay $22 CAD. They in turn generate an official document which you must present to the RF on the day you enter Brasil. The intent is to prove that you legitimately lived here with bank statements, rental contracts, etc, etc for a period of over a year in order to either return to Brasil or immigrate and bring your assets into the country tax free. You have 90 days prior and 180 after your entry date to do so.
If you don't do this form you will have a significant tax problem. The process is a time consuming PITA and somewhat expensive with all the fees, but, the fines are 1,000X worse if you don't do it.
YMMV based on your country.