markdown2plaintext_forGoogleDocs.gs

function convertMarkdownToPlainText() {
  // Get the active document and body
  var body = DocumentApp.getActiveDocument().getBody();

  // Retrieve the text from the document
  var text = body.getText();

  // Replace common Markdown patterns with plain text equivalents
  text = text.replace(/__([^_]+)__/g, '$1'); // bold
  text = text.replace(/\*\*([^\*]+)\*\*/g, '$1'); // bold
  text = text.replace(/_([^_]+)_/g, '$1'); // italic
  text = text.replace(/\*([^\*]+)\*/g, '$1'); // italic
  text = text.replace(/\#\#([^\#]+)\#\#/g, '$1'); // headers
  text = text.replace(/\#\#\#([^\#]+)\#\#\#/g, '$1'); // smaller headers


  // Set the new text
  body.setText(text);
}
function onOpen() {
  var ui = DocumentApp.getUi();
  
  // Create a new menu in Google Docs with a single menu item
  ui.createMenu('Markdown Converter')
      .addItem('Convert to Plain Text', 'convertMarkdownToPlainText')
      .addToUi();
}