Simple gulp task to concatenate markdown to pdf from multiple files to one.

gulpfile.js

/**
 * @description Multi markdown files to pdf.
 * @author Thanos Korakas <thanoskorakas@gmail.com>
 */
var gulp = require('gulp');
var markdownpdf = require('gulp-markdown-pdf');
var concat = require('gulp-concat');

gulp.task('default', function () {
  return gulp.src('path/*.md')
    .pipe(concat('output.pdf'))
    .pipe(markdownpdf())
    .pipe(gulp.dest('dist'));
});