# Adjust Font Size and Flatten Form Fields in PDFs with PdfProcessing

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img[alt$="><"] {
  border: 1px solid lightgrey;
}
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## Environment

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

## Description

Learn how to adjust the font size of textbox fields to fit the whole text content while processing a PDF form.

![Adjust TextBox Font Size ><](https://www.telerik.com/document-processing-libraries/documentation/assets/c8239cb086cea2a69dae184c8925c99c/textboxfield-calculculate-font-size.gif)

## Solution

To auto-size text in [TextBoxFields](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/interactive-forms/form-fields/textboxfield), set the `TextBoxField.TextProperties.FontSize` property to `0`. This allows the font size to adjust automatically to fit the content when the document is **displayed** in a viewer.

```csharp
TextBoxField textBoxField = new TextBoxField("AutoSizeTextBox");
textBoxField.TextProperties.FontSize = 0; // Auto-size when displayed in a PDF viewer
textBoxField.TextProperties.Font = FontsRepository.HelveticaBold;
textBoxField.Value = "Sample text for auto-sizing.";
```

However, to adjust the font size and flatten the [form fields](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/interactive-forms/form-fields/formfields) to produce a non-editable PDF document, you need to calculate the appropriate font size according to the rectangle occupied by the [widget](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/annotations/widgets).

The following code snippet shows how to calculate the font size manually to fit the content:

```csharp
public static double CalculateFontSizeForRectangle(string text, Rect rect, FontBase font)
{
    double fontSize = 0;
    Size measuredSize = new Size(0, 0);
    Size availableSize = rect.Size;

    while (measuredSize.Width < availableSize.Width && measuredSize.Height < availableSize.Height)
    {
        fontSize++;
        Block block = new Block();
        block.TextProperties.FontSize = fontSize;
        block.TextProperties.Font = font;
        block.InsertText(text);
        measuredSize = block.Measure();
    }

    return fontSize - 1;
}
```

Use this calculated font size to create the textbox field:

```csharp
        static void Main(string[] args)
        {
            RadFixedDocument document = new RadFixedDocument();
            RadFixedPage page = document.Pages.AddPage(); 
            FontBase font = FontsRepository.Helvetica;
            string wideText = "This is a wide textbox that demonstrates horizontal fitting of text content.";
            Rect wideRect = new Rect(200, 500, 400, 30);
            double wideFontSize = CalculateFontSizeForRectangle(wideText, wideRect, font);

            TextBoxField wideTextBoxField = CreateTextBoxWithCalculatedFont("WideTextBox", wideText, wideRect, wideFontSize, font);
            document.AcroForm.FormFields.Add(wideTextBoxField);
            var wideWidget = wideTextBoxField.Widgets.First();
            page.Annotations.Add(wideWidget);
            wideWidget.RecalculateContent();
            string outputPath = "AutoSizeTextBoxForm.pdf";
            using (FileStream output = File.Create(outputPath))
            {
                PdfFormatProvider provider = new PdfFormatProvider();
                provider.Export(document, output, TimeSpan.FromSeconds(10));
            }

            Process.Start(new ProcessStartInfo() { FileName = outputPath, UseShellExecute = true });
          
        }

        /// <summary>
        /// Creates a TextBoxField with calculated font size for the given rectangle
        /// </summary>
        private static TextBoxField CreateTextBoxWithCalculatedFont(string name, string text, Rect rect, double fontSize, FontBase font)
        {
            TextBoxField field = new TextBoxField(name);
       
            field.TextProperties.FontSize = Unit.DipToPoint(fontSize);
            field.TextProperties.Font = font;
            field.Value = text;

            var widget = field.Widgets.AddWidget();
            widget.Rect = rect;
            widget.Border.Width = 0;
            widget.TextProperties.FontSize = Unit.DipToPoint(fontSize); ;
            widget.TextProperties.Font = font;

            return field;
        }

        /// <summary>
        /// Calculates the optimal font size for text to fit within a specific rectangle
        /// </summary>
        public static double CalculateFontSizeForRectangle(string text, Rect rect, FontBase font)
        {
            double fontSize = 0;
            Size measuredSize = new Size(0, 0);
            Size availableSize = rect.Size;
            while (measuredSize.Width<availableSize.Width && measuredSize.Height< availableSize.Height)
            {
                fontSize++;
                Block block = new Block();
                block.TextProperties.FontSize = fontSize;
                block.TextProperties.Font = font;
                block.InsertText(text);
                measuredSize = block.Measure();
            }

            return fontSize-1;
        }
```

## See Also

* [PdfProcessing Overview](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/overview)
* [Flatten Form Fields](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/flatten-form-fields)
* [TextBoxFields](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/interactive-forms/form-fields/textboxfield)
* [Widget](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/annotations/widgets)