Create PowerPoint presentation using PowerPoint template

Introduction

The article tells how to create PowerPoint presentation using PowerPoint template and Office OpenXML SDK 2.0. I assume the users have basic knowledge about Office OpenXML. 

Background  

To do so, first we need an existing PowerPoint template (*.potx file).  

Using the code 

1. Create a simple .potx file.

Open Microsoft PowerPoint Presentation. The left panel contains a default slide, delete it. On the File menu, click Save As. In the File name box, type a name for your template, and then, in the Save as type box, select PowerPoint Template(*.potx). Let’s name this template as SimplePresentationTemplate.potx.

2. Copy this template into a MemoryStream.
C#

MemoryStream templateStream = null;             
using (Stream stream = File.Open("SimplePresentationTemplate.potx", FileMode.Open, FileAccess.Read)) 
{ 
    templateStream = new MemoryStream((int)stream.Length); 
    stream.Copy(templateStream);  
    templateStream.Position = 0L; 
}

stream.Copy(templateStream) copies the FileStream into the MemoryStream. This is an extension method. 

C#

public static void Copy(this Stream source, Stream target) 
{ 
    if (source != null) 
    { 
        MemoryStream mstream = source as MemoryStream; 
        if (mstream != null) mstream.WriteTo(target); 
        else 
        { 
            byte[] buffer = new byte[2048]; // this array length is sufficient for simple files 
            int length = buffer.Length, size; 
            while ((size = source.Read(buffer, 0, length)) != 0) 
                target.Write(buffer, 0, size); 
        } 
    } 
}

3. Create presentation file using the stream.
C#

using (PresentationDocument prstDoc = PresentationDocument.Open(templateStream, true)) 
{ 
        prstDoc.ChangeDocumentType(DocumentFormat.OpenXml.PresentationDocumentType.Presentation);
        PresentationPart presPart = prstDoc.PresentationPart; 
        presPart.PresentationPropertiesPart.AddExternalRelationship(
          "http://schemas.openxmlformats.org/officeDocument/2006/" + 
          "relationships/attachedTemplate", 
          new Uri(("SimplePresentationTemplate.potx", UriKind.Absolute));
        presPart.Presentation.Save(); 
}

4. Save the memory stream into a file:
C#

File.WriteAllBytes("PresentationFile1.pptx", presentationStream.ToArray());

That’s it.. The presentation file PresentationFile1.pptx got created without altering the template file.