I believe one of the hotel staff (being a busybody) stapled my departure slip to one of the pages inside my passport. Now i could see two small staple holes on one of the pages inside the passport.

I ponder if the passport is still valid because I thought I read somewhere that the passport should not be tampered in any way.

So, i also ponder let's say if there is coffee stain on the passport or if the passport is dog-eared, is it still valid? Because I always keep my passport in good condition.