Download the file into Specific local system directory from file management URL

public static void main(Args _args)
{
        DocuRef                     docuReference;
        DocuValue                   docuValue;
        DocuAction                  docuActionClass;
        str                               url;
        Browser                     br = new Browser();
        var                         generator = new Microsoft.Dynamics.AX.Framework.Utilities.UrlHelper.UrlGenerator();

       
       docuReference = DocuRef::find(curExt(), RefRecId) // select the DocuRef table buffer record.

        if(docuReference)
        {
                docuValue = docuReference.docuValue();               
                 url = docuValue.Path;

                if (!url || docuValue.Type == DocuValueType::Others)
                {
                    str accessToken = DocumentManagement::createAccessToken(docuReference);
                    url =           Microsoft.Dynamics.AX.Framework.FileManagement.URLBuilderUtilities::GetDownloadUrl(docuValue.FileId, accessToken);
                } // getting only file management URL without Host.

                var currentHost   = new System.Uri(UrlUtility::getUrl());

                generator.HostUrl = currentHost.GetLeftPart(System.UriPartial::Authority);  
               // this above code is used to find the Host URL; for example, url = "https:usnconeboxax1aos.cloud.onebox.dynamics.com/"; 

                url = generator.HostUrl+"/"+ url;
  
                System.Net.WebClient wc = new System.Net.WebClient();

                wc.DownloadFile(url, @"C:\myfile.xlsx"); // specify the file path in second parameter.


If you want to convert this file into IO Stream (Memory stream): Use below code.

               System.IO.Stream        stream = File::UseFileFromURL(url);

Convert this stream into file again:

              var fileStream = new System.IO.FileStream(@"C:\myfile1.xlsx.", System.IO.FileMode::Create, System.IO.FileAccess::Write);
                stream.CopyTo(fileStream);

          }
}