message: Include the default viewers in
diff: @@ -143,7 +143,22 @@ export class Viewer {
  openExternal(sourceFile: string) {
  const pdfFile = this.extension.manager.tex2pdf(sourceFile)
  const configuration = vscode.workspace.getConfiguration('latex-workshop')
  - const command = JSON.parse(JSON.stringify(configuration.get('view.pdf.external.command'))) as ExternalCommand
  + let command = JSON.parse(JSON.stringify(configuration.get('view.pdf.external.command'))) as ExternalCommand
  + if (!command.command) {
  + switch (process.platform) {
  + case 'win32':
  + command = {'command': 'SumatraPDF.exe', 'args': ['%PDF%'] }
  + break
  + case 'linux':
  + command = {'command': 'xdg-open', 'args': ['%PDF%'] }
  + break
  + case 'darwin':
  + command = {'command': 'open', 'args': ['%PDF%'] }
  + break
  + default:
  + break
  + }
  + }
  if (command.args) {
  command.args = command.args.map(arg => arg.replace('%PDF%', pdfFile))
  }
  