having problem with reading docx and pptx files from access attachmant field - vb.net

Question

I have a program that stores files in a attachment field in access database.
Here's the code I use to insert files:
Imports Microsoft.Office.Interop.Access.Dao
Private Sub insert_file(ByVal path As String)
Dim dbe As New DBEngine
Dim db As Database = dbe.OpenDatabase(My.Application.Info.DirectoryPath &"\Mydatabase.accdb")
Dim rstrecord As Recordset = db.OpenRecordset("select * from tblfiles where id=1", RecordsetTypeEnum.dbOpenDynaset)
rstrecord.Edit()
Dim rstattachments As Recordset2 = rstrecord.Fields("File").Value
rstattachments.AddNew()
Dim attachmentdata As Field2 = rstattachments.Fields("FileData")
attachmentdata.LoadFromFile(path)
rstattachments.Update()
rstattachments.Close()
rstrecord.Update()
rstrecord.Close()
db.Close()
End Sub
and I have a option to export the files.Here is the code:
Private Sub export(ByVal id As Integer, ByVal filestr As String, path As String)
DS.Reset()
con = New OleDbConnection(strcon)
con.Open()
cmdtxt = "SELECT ID, File.FileName,File.FileType, File.FileData FROM tblfiles where ID=" & id & " and File.FileName = '" & filestr & "' "
DA = New OleDbDataAdapter(cmdtxt, con)
DA.Fill(DS, "tblfiles")
con.Close()
Dim savestr As String = path
Dim byt() As Byte = DS.Tables("tblfiles").Rows(0).Item("File.FileData")
Try
File.WriteAllBytes(savestr, byt)
MessageBox.Show(File exported successfully)
Catch ex As Exception
messagebox.show(ex.message)
End Try
End Sub
There is no error in inserting and exporting files but when I export pptx and docx files and I open them I receive the following messages:
docx:The file is corrupt and can not be open.
pptx:powerpoint found a problem with content in file.powerpoint can attempt to repair the presentation.