how to find a file path of a particular file in program folder c#

A solution using 'EnumerateFiles, which may be faster than using 'GetFiles:

private bool findFilePath(string directoryPath, string fileName, out string result)
{
    string fullPath = Path.Combine(directoryPath, fileName);

    if (File.Exists(fullPath))
    {
        result = fullPath;
        return true;
    }

    // note this initialization required here
    // since 'result has been passed by reference using 'out
    result = string.Empty;

    try
    {
        result = Directory.EnumerateFiles(directoryPath, fileName, SearchOption.AllDirectories).First();
    }
    catch
    {
        // something went wrong ...
        return false;
    }

    // valid result
    return true;

Example of calling this method:

// note that 'result is passed by reference
string result;

if (findFilePath(@"C:\Program Files", @"CASdb.accdb", out result))
{
    // result contains path to file
}

Discussion:

First, note that there are some Directories in the boot-drive 'Program Files folder, like 'WindowsApps, that you cannot access with either 'GetFiles or 'EnumerateFiles unless you have the access right of "TrustedInstaller." For example with Win 8 see:[^]. Trying to access directories with TrustedInstaller status will result in an application breaking error.

For how to create "TrustedInstaller" access (manually) in the FileExplorer: [^].

Getting this kind of permission in C# code is complex: start here to get oriented: [^], and then see: [^], [^].

Modifying TrustedInstaller status directory access is probably something you should not be doing for security reasons ... unless you are a legitimate SysAdmin. Get ready for some serious study if you need to take this on !

This is another approach that will stop searching when the file is found.

string foundFilePath = FindFile(@"C:\Program Files", "CASdb.accdb");

Note that this method is recursive

private string FindFile(string directory, string fileName)
{
    string foundFileName = null;
    try
    {
        foundFileName = Directory.GetFiles(directory, fileName).FirstOrDefault();
        if (String.IsNullOrEmpty(foundFileName))
        {
            foreach (string dir in Directory.GetDirectories(directory))
            {
                foundFileName = FindFile(dir, fileName);
                if (!String.IsNullOrEmpty(foundFileName))
                    break;
            }
        }
    }
    catch { } // The most likely exception is UnauthorizedAccessException
              // and there is not much to do about that

    return foundFileName;
}

I have not done any bench marking to see if this way is faster or not.