Create Minecraft texturepack yourself (error)?

ev
- in Textures
2

I tried to create a texture pack for minecraft myself, it says on the Internet that I should take the standard minecraft texturepack as a template and drag it to paint.net to edit it there. Unfortunately it always says that it is not the correct image format, so that I can't open it in Paint. Can anyone help me with this?

Create Minecraft texturepack yourself error
Cu

I guess the file is in the ZIP file because it says .ZIP and not png

ev

Okay, then I already know why, can I change the file somehow?