首先將接收到的 byte array寫入至MemoryStream 再藉由MemoryStream寫入至FileStream(在初始時順帶指定存入至硬碟路徑) 最後記得沒用的Stream都要關閉以及釋放 byte[] fileData = restRes.RawBytes; MemoryStream ms = new MemoryStream(); ms.Write(fileData, 0, fileData.Length); ms.Seek(0, SeekOrigin.Begin); FileStream fileStream = new FileStream(CurDProjectDir + @"\TestData\test.pdf", FileMode.Create); ms.WriteTo(fileStream); fileStream.Close(); fileStream.Dispose(); ms.Close(); ms.Dispose(); Ref: Save and load MemoryStream to/from a file https://stackoverflow.com/questions/8624071/save-and-load-memorystream-to-from-a-file Convert a Byte Array to a Stream in C# https://medium.com/@stevenscript/convert-a-byte-array-to-a-stream-in-c-840889a59174 How do I convert struct System.Byte byte[] to a System.IO.Stream object in C#? https://stackoverflow.com/questions/4736155/how-do-i-convert-struct-system-byte-byte-to-a-system-io-stream-object-in-c/4736185
