The Cadastro Nacional da Pessoa Jurídica, which is Portuguese for National Registry of Legal Entities or most commonly known as CNPJ, has functions similar to those of the CPF. The only difference being that it is unique to the use of legal entities. The CNPJ is a number that identifies these legal entities and other legal arrangements at the Federal Revenue Service.
The CNPJ must be detailed on all invoice and receipts issued by the company and must also be detailed on the packaging of any products manufactured by the company.(wikipedia)
The CNPJ registration number has a total of 14 digits. The first 8 digits are the registration number, the following 4 digits identify the entity branch, for example 0001 for headquarters and the following numbers indicate the sequence of branches of a company. The last 2 digits form a checksum of the 12 previous digits.
This tool was developed for programmers and testers who have the constant need to enter different CNPJ numbers in developing forms.