Is my NIF permanent?
Yes, it is!
Your NIF is a document that never expires and if you lose your 'Finanças' document, even though you can request a new paper, your NIF remains the same.
Is it enough to have a .pdf file of the NIF?
Yes!
The NIF is a simple white paper that will be sent to you via .pdf file. It's important to note that there are no government seals or stamps on it. If you requested directly in Portugal, the file would be the same, as the .pdf document printed at home.
Though the document sent to you by Finanças via AnchorLess may have an expiration date on the upper right section (within the Government Protocol information) and the term 'Provisório' (temporary), this is simply an estimation of when you can request a 'Contribuinte' (taxpayer) card.
What is a taxpayer card?
The taxpayer card is not obligatory. We do not recommend you request one, as the PDF document sent by Finanças will always be accepted. Usually just informing your NIF number to the services that it will be requested is enough, without the need to present the document (except in Bank agencies).
The card can be requested on 'e-balcão', and it's free. It is another paper that you must cut in the format of a credit card and it is commonly used by older Portuguese people.
To request your NIF card, visit this article, which summarizes the procedure.