Basic Qn: F4 to open file in PSPad

How can I set F4 to open the selected file(s) in PSPad?

If multiple files are selected before pressing F4, they should be open in tabs in PSPad.

Thanks in advance.

Settings->Customize->Hot Keys.

Add a hotkey which runs

"C:\Path\to\PSPPad.exe" {allfilepath}

Assuming PSPPad works like most other editors and can take more than one filename on the command-line.