WordPress Download Manager gives you a verity way of attaching files, you can upload from your pc or use server file browser to explore files in the server and attach from there or attach an URL from any remote location, also you can use WordPress Download Manager Cloud Storage add-ons if you want to keep your files in cloud storage like Amazon S3, Google Drive, Dropbox, Box.com or One Drive and serve the downloads from your site. And in WordPress download manager, you can use those cloud storage altogether and which gives you lots of free storage and bandwidth.
Attach File section provides you several ways to attach files with your package.
You can upload files from your local computer by clicking “SELECT FILES” button or by dragging files into the marked drop zone. You can select one or more files at a time and click "Open". The upload will start immediately. You’ll see a progress bar for each file upload.
You can use remote URL as a file source using this option and you can add multiple URLs with the same package. Simply add URL in the textbox showing below the file upload/drop zone, and click the button with "+" sign
Click "SELECT FROM SERVER" button to open the server file browser. you can browse files from your server and add them to your package. You need to select the file browser root directory from the download manager settings page. if you don’t set root directory then default root will be your WordPress base dir.
After adding files, your files will be displayed under the "Attached Files" section for further modifications.
Also, you can attach a directory path to your download manager package:
You can use the server directory browser to browse and select directory:
And, you can add, edit or delete any file in that directly from FTP or any other way, and any modification in that directory will be applied on package download automatically.
And at front-end you can show the file list of attached directory like this:
You can also attach files from Dropbox, Google Drive, Amazon S3 using the cloud storage add-ons here:
https://www.wpdownloadmanager.com/downloads/cloud-storage/
For any technical issue, if you are already using pro version please post in pro forum and free version users please post in free forum. Otherwise, if you have any pre-sale or order related query please contact live chat support team. For technical support.