> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/uwp/get-started/samples/visualcomparisontest.md).

# VisualComparisonTest

Sample C# code for using Apryse SDK to overlay two PDF files allowing for a visual color difference between them. This is commonly used to see changes between two document revisions or in drawing blue

Sample C# code for using Apryse SDK to overlay two PDF files allowing for a visual color difference between them. This is commonly used to see changes between two document revisions or in drawing blueprints that are overlayed with updated data.

{% tabs %}
{% tab title="C#" %}
{% code lineNumbers="true" %}

```csharp
//
// Copyright (c) 2001-2020 by PDFTron Systems Inc. All Rights Reserved.
//

using System;
using System.IO;
using System.Threading.Tasks;
using Windows.Foundation;

using pdftron.PDF;
using pdftron.SDF;

using PDFNetUniversalSamples.ViewModels;

namespace PDFNetSamples
{
    public sealed class VisualComparisionTest : Sample
    {
        public VisualComparisionTest() :
            base("VisualComparision", "PDFNet can generate a visual comparison between two different documents. The comparison result itself is a resolution independent PDF -- well suited for adding high-quality diff support into existing app workflows.")
        {
        }

        public override IAsyncAction RunAsync()
        {
            return Task.Run(new System.Action(async () => {
                WriteLine("--------------------------------");
                WriteLine("Starting Visual Comparision Test...");
                WriteLine("--------------------------------\n");

                bool error = await DiffingTestAsync();

                if (error)
                {
                    WriteLine("Visual Comparision failed");
                }
                else
                {
                    WriteLine("Visual Comparision succeeded");
                }

                WriteLine("\n--------------------------------");
                WriteLine("Done Visual Comparision Test.");
                WriteLine("--------------------------------\n");
            })).AsAsyncAction();
        }

        private async Task<bool> DiffingTestAsync()
        {
            bool error = false;

            string firstDocumentPath = Path.Combine(InputPath, "diff_doc_1.pdf");
            string secondDocumentPath = Path.Combine(InputPath, "diff_doc_2.pdf");
            string outputDocumentPath = Path.Combine(OutputPath, "VisualComparision.pdf");

            if ((!File.Exists(firstDocumentPath)) || (!File.Exists(secondDocumentPath)))
            {
                WriteLine("Atleast one input file does not exist. Aborting.");
                error = true;
                return error;
            }

            try
            {
				using (PDFDoc firstDocument = new PDFDoc(firstDocumentPath))
				using (PDFDoc secondDocument = new PDFDoc(secondDocumentPath))
				{
					Page firstDocumentPage = firstDocument.GetPage(1);
					Page secondDocumentPage = secondDocument.GetPage(1);

					DiffOptions diffOptions = new DiffOptions();
					diffOptions.SetColorA(new ColorPt(1, 0, 0));
					diffOptions.SetColorB(new ColorPt(0, 0, 0));
					diffOptions.SetBlendMode(GStateBlendMode.e_bl_normal);

					PDFDoc outputDocument = new PDFDoc();
					outputDocument.AppendVisualDiff(firstDocumentPage, secondDocumentPage, diffOptions);
					await outputDocument.SaveAsync(outputDocumentPath, SDFDocSaveOptions.e_linearized);
                    await AddFileToOutputList(outputDocumentPath).ConfigureAwait(false);
                }
            }
            catch (Exception e)
            {
                WriteLine(GetExceptionMessage(e));
                error = true;
            }

            return error;
        }
    }
}
```

{% endcode %}
{% endtab %}
{% endtabs %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.apryse.com/uwp/get-started/samples/visualcomparisontest.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.