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Invert PDF Document Colors
Updated on Jun 9, 2026
Environment
| Product Version | Product | Author |
|---|---|---|
| 2021.1.322 | RadPdfProcessing | Martin Velikov |
Description
This article describes how to invert the background and text colors within a PDF document by iterating its content.
Solution
The following code snippets demonstrate how to import a PDF document and invert its background and text color by iterating its content.
Example 1: Import a PDF File and Invert Its Background and Content Color
csharp
RadFixedDocument document;
PdfFormatProvider provider = new PdfFormatProvider();
using (Stream input = File.OpenRead(path))
{
document = provider.Import(input);
}
TextColor = RgbColors.White;
BackGroundColor = RgbColors.Black;
InvertBackgroundColor(document);
InvertContentColor(document);
string exportedDocument = "ExportedDocument6.pdf";
if (File.Exists(exportedDocument))
{
File.Delete(exportedDocument);
}
using (Stream output = File.OpenWrite(exportedDocument))
{
provider.Export(document, output);
}The PDF document has no background concept. To achieve the inverted background, create a RectangleGeometry by using the page size and setting the desired color to it.
Example 2: Invert the Document Background Color
csharp
private static void InvertBackgroundColor(RadFixedDocument document)
{
foreach (RadFixedPage page in document.Pages)
{
Graphics.Path path = new Graphics.Path();
path.Fill = BackGroundColor;
Graphics.RectangleGeometry rectangle = new Graphics.RectangleGeometry(page.MediaBox);
path.Geometry = rectangle;
page.Content.Insert(0, path);
}
}The following methods invert the document elements' color by recursively iterating their content and setting the desired color through the relevant Fill property.
Example 3: Invert the Document Content Color
csharp
private static void InvertContentColor(RadFixedDocument document)
{
foreach (RadFixedPage page in document.Pages)
{
InvertCollectionColors(page.Content);
}
}
private static void InvertCollectionColors(ContentElementCollection contentElementCollection)
{
foreach (ContentElementBase contentElement in contentElementCollection)
{
if (contentElement is TextFragment textFragment)
{
textFragment.Fill = TextColor;
}
else if (contentElement is Graphics.Path path && path.Fill.Equals(TextColor))
{
path.Fill = BackGroundColor;
}
else if (contentElement is Form form)
{
InvertCollectionColors(form.FormSource.Content);
}
}
}