gulpfile.js

var gulp = require('gulp');
var exec = require('gulp-exec');

gulp.task('pandoc', function() {
  var options = {
    silent: true
  };
  gulp.src('./input.md')
    .pipe(exec('pandoc <%= file.path %> -f markdown -o output.docx', options))
    .pipe(exec('pandoc <%= file.path %> -f markdown -o output.pdf -V documentclass=ltjarticle -V classoption=a4j -V classoption=landscape --latex-engine=lualatex --toc', options));
});

gulp.task('watch', function() {
    gulp.watch('./input.md', function(event) {
        gulp.run('pandoc');
    });
});