When we cut from various sources and paste into the destination document, we often end up with a mish mash of our originally formatted content and foreign content. Here are some techniques to reduce the pain.
When you right click to paste
Left icon - K - Keep Source Formatting
Middle icon - M - Merge Formatting
Right icon - T - Keep Text Only or
Ctrl+Shift+Y - Paste as Plain Text
After you paste
Setting your preferences for repeated use
File > Options > Advanced > Cut, Copy,, and Paste
Microsoft documentation: Control the formatting when you paste text
Removing Styles and Direct Formatting long after the Paste
Note the virtual entry in the Styles Pane - Clear All - it isn't real Style, it is an menu item to clear styles and direct formatting.
Google Docs Paste Behaviour
Ctrl+V - Pastes with Source Formatting
Ctrl+Shift+V - Pastes plain text