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You can change the version of any PDF file by using Document.Convert method as in the code snippet below. We have attached generated PDF file for your kind reference. Test_1.3.pdf
//load PDF document
Document doc = new Document(dataDir + "6-29 Revised Manuscript.pdf");
// set the PDF file version
doc.Convert(new MemoryStream(), PdfFormat.v_1_3, ConvertErrorAction.Delete);
// save updated file
doc.Save(dataDir + "Test_1.3.pdf");
We hope this will be helpful. Please feel free to contact us if you need any further assistance.