⌛ Quick question about US pension cheques

Pedro,
Yes you are required by law to file an income tax return. Since you will be collecting social security they will know about it. It is highly unlikely that you will have to pay tax though.
A more complicated situation is the tax consequences of working overseas. US citizens resident outside the US and working outside the US can deduct the first $80,000 or so. This is subject to change and may already have changed. Also the US has agreements with many countries to not double tax you. If you are taxed in the country you are working or living in your US tax liability may be reduced. It has been a few years since I have been in this situation so my info may be out of date. What all this means is you should sit down with a real tax professional familiar with overseas workers. Don't make decisions based on my advice or other well meaning non professionals, and you need someone more qualified than the local H&R Block tax preparer.