Thaw puff pastry squares, covered, at room temperature 15-30 minutes until flexible or overnight refrigerated.
Add cream cheese and powdered sugar to bowl of mixer fitted with paddle attachment; mix on low speed for 1-2 minutes or until smooth.
Stop mixer, scrape bowl and paddle; add flour and vanilla extract.
Mix for 1 additional minute; refrigerate until needed.
Brush puff pastry squares with water and press into sugar; cut into 4 equal squares.
Place on parchment-lined sheet pan, sugar side down; brush edges with water.
Add cream cheese filling to pastry bag and pipe a line diagonally across pastry.
Add guava paste to separate pastry bag and knead to make piping easier; pipe a line on top of cream cheese filling.
Lift a corner of puff pastry and fold over filling; take opposite corner and fold on top, tucking end underneath to seal.