Can I remove official documents stapled into my passport?

I disagree with the other answer. My passport is a cheese full of staple holes. Authorities from all other the world (especially Japan immigration officers who are quite keen on staples) have attached and detached countless pieces of paper to/from my passport over the years. Tax-free receipts, immigration cards, permits of all kinds, anything. Some are still there, some are not. I have never been asked a single question about that, by any country, over my latest 15+ international trips. As long as your passport is legit and you can explain everything, I would not worry too much about it. Seriously, most passports are full of holes. This cannot be a red flag per se, otherwise you get half of people arrested. I cannot imagine a scene where some officer takes you to an investigation room just for ‘that staple in your passport’. He will have other concerns for sure. What’s more, many countries don’t even stamp passports or leave a record of your travel at all. Passports are very bad travel records to begin with. That being said, I strongly advise against removing a visa (which could be a red flag).

I wouldn't, as similar questions ("Can I remove “attention” sticky note in passport" for example) have resulted in answers with personal experiences where the absence of something which has obviously previously existed in your passport has raised the concern of an immigration official.

As 2 other answers are already stating 2 opposite viewpoints and there are certainly 2 major quite opposite opinions, my advice would be, if in doubt, to leave the removal of these stapled documents to the officers.

If you're told that you don't have blank pages in your passport, ask them to remove the old stapled documents from those pages or do it yourself in front of the officer. This way you won't be considered hiding anything and you'll have free space in your passport. At least this is what I have done before I could get a new passport.