Adjust Font Size and Flatten Form Fields in PDFs with PdfProcessing
Environment
| Version | Product | Author |
|---|---|---|
| 2025.3.806 | RadPdfProcessing | Desislava Yordanova |
Description
Learn how to adjust the font size of textbox fields to fit the whole text content while processing a PDF form.
Solution
To auto-size text in TextBoxFields, set the TextBoxField.TextProperties.FontSize property to 0. This enables the font size to adjust automatically to fit the content when the document is displayed in a viewer.
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, if you want to adjust the font size and flatten the form fields to produce a non-editable PDF document, it would be necessary to calculate the appropriate font size according to the rectangle occupied by the widget.
The following code snippet shows how to calculate the font size manually to fit the content using the following approach:
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:
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;
}