# Preserving Original Bold, Italic and Regular Fonts When Exporting PDF Documents Using PdfProcessing  in .NET Standard

## Environment

| Version    | Product          | Author                                                                          |
| ---------- | ---------------- | ------------------------------------------------------------------------------- |
| 2025.3.806 | RadPdfProcessing | [Desislava Yordanova](https://www.telerik.com/blogs/author/desislava-yordanova) |

## Description

When you use the [PdfProcessing](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/overview) library in .NET Standard to embed fonts into a PDF, the library can unintentionally substitute fonts for text content and fields that already use a different font. The .NET Standard environment requires font data to be explicitly provided for embedding. The .NET Framework can access system fonts directly, but .NET Standard cannot.

Without the required font files, the library substitutes missing fonts and can alter the PDF appearance. This issue commonly arises when the font chosen for embedding replaces existing fonts in the document. For example, the library may convert Arial text to Courier New, which results in illegible text in certain languages.

This knowledge base article also answers the following questions:

* How can I prevent font substitution in PdfProcessing while embedding fonts?
* How do I embed fonts without altering the text appearance in PdfProcessing?
* How do I manage fonts dynamically when embedding them in PdfProcessing?

## Solution

To prevent font substitution for text content and fields that must retain their original fonts and style during the embedding process, implement a custom `FontsProvider`. This provider dynamically supplies font data based on the font name and properties found in your PDF.

Follow these steps:

1. Create a custom [FontsProvider](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/cross-platform/fonts) by inheriting from `FontsProviderBase`.
2. Implement the `GetFontData` method to dynamically return font data based on the font properties.
3. Optionally, maintain a repository of commonly used fonts to automate font discovery.

The following example shows a dynamic `FontsProvider` implementation:

```csharp
public class FontsProvider : Telerik.Windows.Documents.Extensibility.FontsProviderBase
{
    public override byte[] GetFontData(Telerik.Windows.Documents.Core.Fonts.FontProperties fontProperties)
    {
        string fontFolder = Environment.GetFolderPath(Environment.SpecialFolder.Fonts);
        string fontFileName = GetFontFileName(fontProperties);

        string fontPath = Path.Combine(fontFolder, fontFileName);
        if (File.Exists(fontPath))
        {
            return File.ReadAllBytes(fontPath);
        }

        return null;
    }

    private string GetFontFileName(Telerik.Windows.Documents.Core.Fonts.FontProperties fontProperties)
    {
        string family = fontProperties.FontFamilyName.ToLowerInvariant();
        bool isBold = fontProperties.FontWeight == FontWeights.Bold;
        bool isItalic = fontProperties.FontStyle == FontStyles.Italic;

        // Mapping for known fonts
        if (family == "courier new")
        {
            if (isBold && isItalic) return "courbi.ttf";
            if (isBold) return "courbd.ttf";
            if (isItalic) return "couri.ttf";
            return "cour.ttf";
        }

        // Generic fallback: try to construct filename from family and style
        string suffix = "";
        if (isBold && isItalic) suffix = "bi";
        else if (isBold) suffix = "bd";
        else if (isItalic) suffix = "i";

        return $"{family}{suffix}.ttf";
    }
}
```

### Applying the Fonts Provider

```csharp
Telerik.Windows.Documents.Extensibility.FontsProviderBase fontsProvider = new FontsProvider();
Telerik.Windows.Documents.Extensibility.FixedExtensibilityManager.FontsProvider = fontsProvider;
```

### Notes

* Ensure the required font files are installed on your machine or stored locally in a specified directory.
* For automation, maintain a repository of commonly used fonts and expand it as new fonts are encountered.
* This implementation handles font data dynamically based on the document font properties. Avoid hardcoding specific font names wherever possible.

## See Also

* [Implementing a FontsProvider](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/concepts/fonts)