Here is a basic example of how you could combine a compressed file and an executable file in C#:

using System;
using System.IO;
using System.IO.Compression;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Path to the compressed file
            string compressedFilePath = "path/to/compressed/file.zip";

            // Path to the executable file
            string exeFilePath = "path/to/exe/file.exe";

            // Create a new zip archive
            using (ZipArchive archive = ZipFile.Open(compressedFilePath, ZipArchiveMode.Update))
            {
                // Add the executable file to the archive
                archive.CreateEntryFromFile(exeFilePath, Path.GetFileName(exeFilePath));
            }
        }
    }
}

In this example, we create a new ZipArchive object by opening the compressed file using ZipFile.Open method. Then, we use the CreateEntryFromFile method to add the executable file to the archive. This will add the executable file to the existing zip archive, effectively combining the two files.

Note that this code assumes that you have already added a reference to the System.IO.Compression namespace in your project. You can do this by right-clicking on your project in the Solution Explorer, selecting "Add" and then "Reference...", and then selecting the System.IO.Compression library from the list of available references.