cannot preserve space between runs

i want to generate a word document as an input i have this string "open packaging conventions" and each word will have a different style the result should be open packaging conventions

WordprocessingDocument document = WordprocessingDocument.Create(
            @"C:\test PFE.docx",
            WordprocessingDocumentType.Document
        );



        MainDocumentPart mainDocumentPart = document.AddMainDocumentPart();


        mainDocumentPart.Document = new Document();
        mainDocumentPart.Document.AddNamespaceDeclaration("ve", "http://schemas.openxmlformats.org/markup-compatibility/2006");
        mainDocumentPart.Document.AddNamespaceDeclaration("o", "urn:schemas-microsoft-com:office:office");
        mainDocumentPart.Document.AddNamespaceDeclaration("r", "http://schemas.openxmlformats.org/officeDocument/2006/relationships");
        mainDocumentPart.Document.AddNamespaceDeclaration("m", "http://schemas.openxmlformats.org/officeDocument/2006/math");
        mainDocumentPart.Document.AddNamespaceDeclaration("v", "urn:schemas-microsoft-com:vml");
        mainDocumentPart.Document.AddNamespaceDeclaration("wp", "http://schemas.openxmlformats.org/drawingml/2006/wordprocessingDrawing");
        mainDocumentPart.Document.AddNamespaceDeclaration("w10", "urn:schemas-microsoft-com:office:word");
        mainDocumentPart.Document.AddNamespaceDeclaration("w", "http://schemas.openxmlformats.org/wordprocessingml/2006/main");
        mainDocumentPart.Document.AddNamespaceDeclaration("wne", "http://schemas.microsoft.com/office/word/2006/wordml");



        Body documentBody = new Body();
        mainDocumentPart.Document.Append(documentBody);


        StyleDefinitionsPart styleDefinitionsPart =
        mainDocumentPart.AddNewPart<StyleDefinitionsPart>();


        FileStream stylesTemplate =
            new FileStream("styles.xml", FileMode.Open, FileAccess.Read);
        styleDefinitionsPart.FeedData(stylesTempla