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' For complete examples and data files, please go to https://github.com/groupdocsmetadata/GroupDocs_Metadata_NET
' initialize PptFormat
Dim pptFormat As New PptFormat(Common.MapSourceFilePath(filePath))

' initialize PptMetadata
Dim metadata As PptMetadata = pptFormat.DocumentProperties

' set property details 
Dim propertyName As String = "New custom property"
Dim propertyValue As String = "Value"

' check if property already exists
If Not metadata.ContainsKey(propertyName) Then
    ' add property
    metadata.Add(propertyName, propertyValue)
End If

' save file in destination folder
pptFormat.Save(Common.MapDestinationFilePath(filePath))