> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/uwp/get-started/faq/add-license.md).

# Add license key

World's #1 PDF SDK Library for Web, Mobile, Server, Desktop

## Getting a production license

Now that you’ve built your application, and tested it in a deployment environment, you might be ready to purchase a license. Please [contact sales](https://apryse.com/form/contact-sales) in order to get a license key.

## Using the license

When you do not want to be in the watermarked demo/trial mode, it is important that you initialize Apryse library with a valid license key before using any Apryse classes.

{% hint style="info" %}
**Please be sure to initialize Apryse SDK before any calls to Apryse APIs.**
{% endhint %}

After `this.InitializeComponent()` of `App.xaml.cs` in your application, add:

{% tabs %}
{% tab title="C#" %}
{% code lineNumbers="true" %}

```csharp
pdftron.PDFNet.Initialize("Insert commercial license key here after purchase");
```

{% endcode %}
{% endtab %}
{% endtabs %}


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