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// For complete examples and data files, please go to https://github.com/groupdocsmetadata/GroupDocs_Metadata_NET
// initialize PdfFormat
PdfFormat pdfFormat = new PdfFormat(Common.MapSourceFilePath(filePath));
                    
// initialize PdfMetadata
PdfMetadata pdfMetadata = pdfFormat.DocumentProperties;
 
//update document property...
pdfMetadata.Author = "New author";
pdfMetadata.Subject = "New subject";
pdfMetadata.CreatedDate = DateTime.Now;

//save output file...
pdfFormat.Save(Common.MapDestinationFilePath(filePath));