This is one of the things that really surprised me when I arrived in Portugal and became a resident: - the enforced disclosure of your social security / identity number / fiscal number requested everywhere and by everyone. This was especially disturbing after all the stories that I have read about identity theft in the international mainstream media. But it is part and parcel of life in Portugal.
All residents and non-resident foreigners with financial affairs in Portugal must obtain a tax card (cartão de contribuinte) and a fiscal number (número de identificação fiscal/NIF).
For example, you will need to have your fiscal number before you can finalise the purchase of property in Portugal.
To get this fiscal number, you need to complete a form at the local tax office (finanças). You will normally be issued with a temporary fiscal number for the first few months and will receive a permanent one, once the purchase of a property is finalised. Your fiscal number must be used in all dealings with the Portuguese tax authorities, when paying property taxes as well as for various other transactions, e.g. without a fiscal number you cannot register the title deed of your purchased property or even open a bank account in Portugal.
All non-residents who own a holiday or second home in Portugal must nominate a local resident (of any nationality) as their fiscal representative.
This representative will receive all official communications from the relevant Portuguese authorities. You can also have your fiscal representative receive your bank statements, ensure that your bank is paying your standing orders (e.g. for utilities and property taxes) and that you have sufficient funds to pay them.
If you let your home in Portugal through a property management company, the above services are normally covered in their service offerings.