This writeup is bases on the following:

  1. A full functional Magento Store.
  2. DownloadPlus and the Import Adapter installed.
  3. Some or all Products to be in your store.

Use the documentation of the Import Adapter to create the Advanced Profile for importing your serialnumbers. You have the following options:

Importing Serialnumbers to Products

The import adapter allows importing serialnumbers and assigning them to products, based on the Products SKU that has to be part of the imported data line. A data line in the imported file thus needs to contain at least:

Example of Importfile with Product SKU and related Serialnumber

You may optional create pools of serialnumbers for one product too while importing:

Example of Importfile with Product SKU, related Serialnumber and product related Serialnumber Pool

Serialnumber pools allow to pull serialnumbers for individual Downloadable Links of the same Product. Per default, if there is no serialnumber pool data in the import, the imported serialnumbers are then used for the whole Downloadable Product.

See also this documentation part oo more about the concept of Serialnumber Pools...

Now import your initial serialnumber data into your store.

To verify the import of your serialnumber data, open one Product through Catalog » Manage Products where data was imported for and select the tab Serialnumbers which will show you the Serialnumbers currently available to the Product:

Importing Serialnumbers into Global Pools

When importing serialnumbers into Global Pools, where these Serialnumbers shall be shared from for multiple products, configure your import adapter accordingly...

Now import your initial serialnumber data into your store.

To verify the import of your serialnumber data, open Catalog » Import storewide Serialnumbers » Available Serialnumbers:

In that list you will see the available Serianumbers and the related Global Pools (if any) these are assigned to.

After the initial import of Serialnumbers you need to tell each Product - you want to use Serialnumbers with - where to assign them from:

For Downloadable Products

Open the Product, open the Downloadable Settings tab and configure the Downloadable Items you have for the product to use Serialnumbers by selecting your option from the Assign Serialnumbers from Pool selection:

Save the product. Now the this Downloadable Product is configured to assign Serialnumbers.

For Simple Products, Virtual Products, all other types of Products

There is nothing additional required to be done on this type of Products, once there are Serialnumbers imported for one if this type of Products these will get assigned for each order automatically.

Please note that for these types of Product Serialnumber pools are not implemented, any Serialnumber Pool data from the import will be ignored and the serialnumbers will be available for the whole Product.

DownloadPlus allows you to define a limit to the Serialnumbers available to a single Product where it sends a notification message to any email address.
To use this feature configure the Downloadable Serialnumbers configuration options as needed and described here...

Per default Serialnumbers purchased with an Order are displayed in the Customer Account only, whenever you want a purchased Serialnumber to be sent via Email then you need to configure the related options here:

System » Configuration » Catalog » Downloadable Serialnumbers

There you also may set if Serialnumbers are downloadble as file and additional options on notifications related to the Serialnumber handling of the extension.

From here on no further actions are required, other than to import new Serialnumber data when needed to add fresh serialnumbers to your products. Through the products being configured for their serialnumbers freshly imported serialnumbers will be used instantly by the products.