You must have seen a rasterization error some time or the other in Photoshop. It normally says, Could not complete the request because the pixels in the type layer cannot be edited without first rasterizing the layer, like this,
This error is displayed when you try to use any painting tools or filters on a layer that has vector data like shape layers, vector masks etc. You must first rasterize the layer that contains the vector data, and then you can use any tools or filters on it.
How to Rasterize a Layer in Photoshop?
Rasterizing a Photoshop layer is very simple. Just select the layer(s) that you want to rasterize and go to Layer > Rasterize > Layer.