Have a 'save as PDF' option

Electron provides this directly. It's easy to do on Mac, but having an explicit option will make it easier on other systems:

https://www.electronjs.org/docs/api/webview-tag#webviewtagprinttopdfoptions

The issue names no files or tests. Start with the linked Electron webview-tag printToPDF documentation, then locate the desktop UI entry point for adding an explicit Save as PDF action. Done means the option works on systems where saving via the Mac UI is not otherwise straightforward.

Written by the indexing model from the issue text.