# CMap Tables

A CMap specifies the mapping from character codes to character selectors and serves the role of a font encoding.

CMaps are usually fully embedded into the PDF document and obtained from it during reading. A CMap can also be defined by a PDF name object, where the name identifies a well-known predefined CMap. The list of predefined CMaps is available in the [Adobe CMap resources repository](https://github.com/adobe-type-tools/cmap-resources).

## Working with Documents Containing Predefined CMap Tables

RadPdfProcessing enables you to use a default implementation for the known predefined CMap tables. You can also create a custom one if you encounter a specific scenario in which the resources are not available for the default class.

## Default Implementation

The **Telerik\[.Windows].Documents.CMapUtils** package provides a default implementation for obtaining the data of a predefined CMap table by a given name. The class that contains implementations for all the CMap tables defined by the PDF Format Specification is called `PredefinedCMapsProvider`. To register an instance of the default implementation, use the `FixedExtensibilityManager` class.

> important To use this feature, you must add a reference to the **Telerik\[.Windows].Documents.CMapUtils package**.

**Register Default CMapsProvider**

```C#

Telerik.Documents.Extensibility.FixedExtensibilityManager.PredefinedCMapsProvider = new PredefinedCMapsProvider();
```

After you register the `PredefinedCMapsProvider` class, you can import any document containing a predefined CMap table.

## Creating a Custom Implementation

The default implementation covers the majority of the scenarios but in some rare cases, you might need to provide a custom CMap. The API enables you to create a custom implementation for a CMap provider so you can provide the data for the custom CMap table. To achieve that, inherit the `PredefinedCMapsProviderBase` abstract class and implement the following members:

| Member                                   | Description                                                                                                                    |
| ---------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------ |
| `byte[] GetCidCMapData(string name)`     | Retrieves the *character code to CID mapping* of a predefined CMap. Returns the CMap resource data for the specified name.     |
| `byte[] GetUnicodeCMapData(string name)` | Retrieves the *character code to Unicode mapping* of a predefined CMap. Returns the CMap resource data for the specified name. |

## See Also

* [FontsRepository API Reference](https://docs.telerik.com/devtools/document-processing/api/Telerik.Windows.Documents.Fixed.Model.Fonts.FontsRepository.html)
* [TextFragment](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/textfragment)