将PDF字符串二进制表示形式转换为PDF

如何将byte()的字符串表示形式从服务器响应转换为PDF?pdf的响应类似于

%PDF-1.4
%����
1 0 obj
<<
/Names 2 0 R.......

我尝试使用Internet上的函数将文本转换为bytes(),曾经它转换为excelent,但现在它不起作用,我不知道为什么。功能如下所示

Private Function TxtToBin(ByVal Str As String) As String
    Dim bt() As Byte = Encoding.Unicode.GetBytes(Str.ToCharArray)
    Dim st As New StringBuilder
    For Each byt As Byte In bt
       st.Append(Convert.ToString(byt, 2).PadLeft(8, "0"c) & " ")
    Next
    Return st.ToString
End Function

并尝试使用下面的代码将该字符串转换为PDF

Dim path_pdf = "some path\test.pdf"
Dim txtBin = TxtToBin("%PDF-1.4 .........")
Dim bytes = System.Text.Encoding.UTF8.GetBytes(txtBin)
File.WriteAllBytes(path_pdf, bytes)

编辑//

Dim message As Task(Of HttpResponseMessage) = client.PostAsync(linkApi, content)
Dim streamResponse = message.Result.Content.ReadAsStreamAsync()
Dim parser = MultipartFormDataParser.Parse(streamResponse.Result)
Dim name_id = parser.GetParameterValue("paramString") //returns string    
Dim pdf_bin= parser.GetParameterValue("PDF") //returns string