--- title: "Highlight a region in a PDF or an image in C#" canonical_url: "https://www.nutrient.io/guides/dotnet/samples/select-pdf-image-region-cs/" md_url: "https://www.nutrient.io/guides/dotnet/samples/select-pdf-image-region-cs.md" last_updated: "2026-05-14T21:57:26.876Z" description: "Learn to draw modifiable highlighted regions on documents using C#. Ideal for anchor and OMR applications. Explore this practical C# code sample!" --- # Highlight a region in a PDF or an image in C# This example shows how to draw highlighted regions on top of a document. A highlighted region is a special feature that’s modifiable by mouse. It can be used to specify areas and highlight them, and it’s especially useful in anchor and OMR applications. [Get Started](https://www.nutrient.io/sdk/dotnet/getting-started.md) [All Samples](https://www.nutrient.io/guides/dotnet/samples.md) [Download](https://www.nutrient.io/guides/dotnet/downloads.md) [Launch Demo](https://www.nutrient.io/demo/) --- ### C# [C#](https://www.nutrient.io/guides/dotnet/samples/select-pdf-image-region-cs.md) ### VB.NET [VB.NET](https://www.nutrient.io/guides/dotnet/samples/select-pdf-image-region-vbnet.md) ```cs //We assume that GdPicture has been correctly installed and unlocked. //We assume the GdViewer object called GdViewer1 has been created and painted on the form. GdPictureImaging oGdPictureImaging = new GdPictureImaging(); //Loading the image from a file. int imageId = oGdPictureImaging.CreateGdPictureImageFromFile("C:\\Image.tif"); //Checking if the image resource has been loaded correctly. if (oGdPictureImaging.GetStat()!= GdPictureStatus.OK) { MessageBox.Show("The image can't be loaded. Error: " + oGdPictureImaging.GetStat().ToString(), "Drawing regions Example", MessageBoxButtons.OK, MessageBoxIcon.Error); } else { //Displaying the image in the GdViewer. GdViewer1.DisplayFromGdPictureImage(imageId); } oGdPictureImaging.Dispose(); //On the Mouse UP event on the GdViewer, create a highlighted region based on the rectangle of selection of the GdViewer. //If no rectangle of selection is painted on the GdViewer, this event will do nothing. public void Mouse_UP_Draw_Region(System.Object eventSender, System.EventArgs eventArgs) { //Initializing variables to hold the position of the rectangle of selection on the document. int leftArea = 0; int topArea = 0; int widthArea = 0; int heightArea = 0; //Checking if a rectangle of selection has been painted on the GdViewer. if (GdViewer1.IsRect()) { //Getting the location of the selection on the document. GdViewer1.GetRectCoordinatesOnDocument(ref leftArea, ref topArea, ref widthArea, ref heightArea); //Setting the ROI on the document: //Adding a region in place of the rectangle of selection. int regionId = GdViewer1.AddRegion("Region", leftArea, topArea, widthArea, heightArea, GdPicture14.ForegroundMixMode.ForegroundMixModeMASKPEN, Color.Green); //Setting region border width. GdViewer1.SetRegionBorderWidth(regionId, 1); //Setting region border color. GdViewer1.SetRegionBorderColor(regionId, Color.Blue); //Redrawing the whole image. GdViewer1.ClearRect(); GdViewer1.Redraw(); } } ``` This code sample is an example that illustrates how to use our SDK. Please adapt it to your specific use case. --- ## Related pages - [Automatically rotate pages of a multipage TIFF file using OCR and VB.NET](/guides/dotnet/samples/auto-rotate-tiff-vbnet.md) - [Automatically rotate pages of a multipage TIFF file using OCR and C#](/guides/dotnet/samples/auto-rotate-tiff-cs.md) - [Convert PDFs, MS Office, and images to TIFF in C#](/guides/dotnet/samples/convert-to-tiff-cs.md) - [Saving images into folders based on their barcode](/guides/dotnet/samples/barcode-auto-sorting-cs.md) - [Saving images into folders based on their barcode](/guides/dotnet/samples/barcode-auto-sorting-vbnet.md) - [Generate a multipage TIFF file using a compression mode per page in C#](/guides/dotnet/samples/create-multipage-tiff-cs.md) - [Converting a Microsoft Word binary file document (DOC) to a Microsoft Word OpenXML document (DOCX) in C#](/guides/dotnet/samples/doc-to-docx-cs.md) - [Merging two PDF documents by alternating pages from both files in VB.NET](/guides/dotnet/samples/merge-pdf-alternate-pages-vbnet.md) - [Using an external OCR engine during PDF/OCR generation](/guides/dotnet/samples/integrate-omnipage-ocr-cs.md) - [Converting a multipage PDF to a multipage TIFF using color detection in C#](/guides/dotnet/samples/pdf-to-tiff-color-detection-cs.md) - [Merging two PDF documents by alternating pages from both files in C#](/guides/dotnet/samples/merge-pdf-alternate-pages-cs.md) - [Converting a multipage PDF to a multipage TIFF using color detection in VB.NET](/guides/dotnet/samples/pdf-to-tiff-color-detection-vbnet.md) - [Recompress existing PDFs using MRC compression in C#](/guides/dotnet/samples/recompress-pdf-mrc-cs.md) - [Recompress an existing PDF using color detection in VB.NET](/guides/dotnet/samples/recompress-pdf-vbnet.md) - [Recompress an existing PDF using color detection in C#](/guides/dotnet/samples/recompress-pdf-cs.md) - [Recompress existing PDFs using MRC compression in VB.NET](/guides/dotnet/samples/recompress-pdf-mrc-vbnet.md) - [Highlight and crop an image in C#](/guides/dotnet/samples/select-image-crop-area-cs.md) - [Highlight and crop an image in VB.NET](/guides/dotnet/samples/select-image-crop-area-vbnet.md) - [Highlight a region in PDF or an image in VB.NET](/guides/dotnet/samples/select-pdf-image-region-vbnet.md) - [Choosing the appropriate OCR zone in C#](/guides/dotnet/samples/select-ocr-zone-cs.md) - [Choosing the appropriate OCR zone in VB.NET](/guides/dotnet/samples/select-ocr-zone-vbnet.md) - [Save bitonal TIFFs with VB.NET using photometric 0](/guides/dotnet/samples/tiff-photometric-vbnet.md) - [Convert a multipage TIFF to a multipage JBIG2 in VB.NET](/guides/dotnet/samples/tiff-to-jbig2-vbnet.md) - [Save bitonal TIFF images with C# and CCITT4](/guides/dotnet/samples/tiff-photometric-cs.md) - [Convert a multipage TIFF to a multipage JBIG2 in C#](/guides/dotnet/samples/tiff-to-jbig2-cs.md)