how to save a byte[] code in pdf/rtf/xps/doc file.(Windows not asp)

byte[] Attachmnt;
Attachmnt = (byte[])dataGridView1.Rows[e.RowIndex].Cells["ResumeData"].Value;
Document1 objDoc = new Document1();           
objDoc.DocContent = Attachmnt;        
FileStream writeStream;
          
File.WriteAllBytes(Application.StartupPath+Resume, objDoc.DocContent);
//Next line is working for .doc extension
writeStream = new FileStream(Application.StartupPath + "Raaz.doc", FileMode.Create);
//Not Working for .pdf and .xps file
writeStream = new FileStream(Application.StartupPath + "File.pdf", FileMode.Create);
writeStream = new FileStream(Application.StartupPath + "Fil1.xps", FileMode.Create);
//In above two line i want help it should be save in pdf or xps file properly and open
//how can we do that user will select his file name with extension through //savefiledialog and then here it should be save as user given
BinaryWriter writeBinay = new BinaryWriter(writeStream);
writeBinay.Write(objDoc.DocContent);
writeBinay.Close();
writeStream.Close();