How to load file from S3 with Presigned URL

Question

I have some folders, sub folders and files in s3. Folder structure is as below.

eg:

 MainFolder
        Subfolder1
           file1.1
           file1.2
           folder1.1
              file1.1.1
           folder1.2
              file1.2.1
        Subfolder2
           file2.1
           file2.2
           folder2.1
              file2.1.1
           folder2.2
              file2.2.1
        Subfolder3
           file3.1
           file3.2
           folder3.1
             file3.1.1
        Subfolder4
           file4.1
           file4.2
 

when I loaded this structure ,when clicking on files, I generated presignedURL

in aspx page

<iframe runat="server" id="iframeFile" 
style="width:600px; height:500px;" frameborder="0">
</iframe>

Code behind:

var request = new GetPreSignedUrlRequest
{
    BucketName = bucketName,
    Key = key,
    Verb = HttpVerb.PUT,
    Expires = DateTime.UtcNow.AddSeconds(30)
};

string url = client.GetPreSignedURL(request);
//string contents = GetContents(url);
iframeFile.Src = url;

I am setting iframeFile.Src = url to show the file, but the file loaded is encrypted. How can we load file?