Editora 0.11.0. Archived, so links from that release keep working. Read the 0.18.5 page →
Editor: Set PDF Page Size…
editor.setPdfPageSize Choose the page size for PDF export (Letter or A4).
How to run it
Open the command palette (M-x in the Emacs keymap) and search for Editor: Set PDF Page Size…, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.