Presentation ppt = new Presentation();
ppt.LoadFromFile(inputFile);
StringBuilder sb = new StringBuilder();
ISlide slide = ppt.Slides[0];
for (int i = 0; i < slide.Shapes.Count; i++)
 {
     IShape shape = slide.Shapes[i];
     if (shape is IAutoShape)
     {
         IAutoShape autoshape = slide.Shapes[i] as IAutoShape;
         string text = autoshape.TextFrame.Text;
         //obtain the text position information
         PointF point = autoshape.TextFrame.GetTextLocation();
         sb.AppendLine("Shape " + i + "：" + text + "\r
" + "location：" + point.ToString());
     }
}
File.AppendAllText(outputFile, sb.ToString());
ppt.Dispose();

Presentation ppt = new Presentation();
ppt.LoadFromFile(inputFile);
ISlide slide = ppt.Slides[0];
IAutoShape autoshape = slide.Shapes[0] as IAutoShape;
IList lines = autoshape.TextFrame.GetLayoutLines();
for (int i = 0; i < lines.Count; i++)
{
   float ascent= lines[i].Ascent;
   float descent = lines[i].Descent;
}

Presentation ppt = new Presentation();
ppt.LoadFromFile("FreeForm.pptx");
ISlide slide = ppt.Slides[0];
int num = 0;
foreach (IShape shape in slide.Shapes)
{
    byte[] svgByte = shape.SaveAsSvg();
    FileStream fs = new FileStream("shape_" + num + ".svg",FileMode.Create);
    fs.Write(svgByte, 0, svgByte.Length);
    fs.Close();
    num++;
}

Presentation ppt = new Presentation();
ppt.LoadFromFile("input.pptx");
ppt.Slides[0].SlideShowTransition.AdvanceAfterTime = 1000;
ppt.Slides[1].SlideShowTransition.SelectedAdvanceAfterTime = false;
ppt.SaveToFile("output.pptx", FileFormat.Pptx2013);
ppt.Dispose();

Previous options:
FromCorner1
FromCorner2
FromCorner3
FromCorner4
New options:
FromTopLeftCorner
FromBottomLeftCorner
FromTopRightCorner
FromBottomRightCorner

Presentation ppt = new Presentation();
ppt.LoadFromFile("input.pptx");
StringBuilder stringBuilder = new StringBuilder();
IAutoShape shape = (ppt.Slides[0].Shapes[0] as GroupShape).Shapes[2] as IAutoShape;
GradientStopCollection stops = shape.Fill.Gradient.GradientStops;
for (int i = 0; i < stops.Count; i++)
{
    float transparency = stops[i].Color.Transparency;
    float brightness = stops[i].Color.Brightness;
    stringBuilder.AppendLine("stops" + i + "transparency: " + transparency + " brightness: " + brightness);
}
File.WriteAllText("output.txt", stringBuilder.ToString());

stops[0].Color.Transparency = 0.5f;
stops[0].Color.Brightness = -0.32f;
ppt.SaveToFile("output.pptx", FileFormat.Auto);
ppt.Dispose();

Presentation ppt = new Presentation();
ppt.LoadFromFile("input.pptx");
DefaultTextRangeProperties format = new DefaultTextRangeProperties();
format.IsBold = TriState.True;
format.Fill.FillType = Spire.Presentation.Drawing.FillFormatType.Solid;
format.Fill.SolidColor.Color = Color.Red;
format.FontHeight = 25;
ppt.ReplaceAndFormatText("Yuma", "AAAA", format);
ppt.SaveToFile("output.pptx",FileFormat.Pptx2016);

presentation.setDefaultFontName("华文行楷");

presentation.resetDefaultFontName();

Spire.Presentation.FileFormat.Pptx2016
Spire.Presentation.FileFormat.Pptx2019

Presentation ppt = new Presentation();
IChart chart = ppt.Slides[0].Shapes.AppendChart(ChartType.ColumnClustered, new RectangleF(50, 50, 400, 400));

//Gets the PrimaryCategory axis
IChartAxis chartAxis = chart.PrimaryCategoryAxis;

//Set "Distance from axis"
chartAxis.LabelsDistance = 200;

//Save to file
ppt.SaveToFile(outputFile, FileFormat.Pptx2013);

Presentation ppt = new Presentation();
ppt.LoadFromFile(inputFile);
IAutoShape shape1 = (IAutoShape)ppt.Slides[0].Shapes[0];
shape1.TextFrame.ColumnCount = 2;
IAutoShape shape2 = (IAutoShape)ppt.Slides[1].Shapes[0];
shape2.TextFrame.ColumnCount = 3;
ppt.SaveToFile(outputFile, FileFormat.Pptx2013);
ppt.Dispose();

Presentation ppt = new Presentation();
ICommentAuthor author = ppt.CommentAuthors.AddAuthor("E-iceblue", "comment");
ppt.Slides[0].AddComment(author, "Add comment", new System.Drawing.Point(18, 25), DateTime.Now);
Comment comment = ppt.Slides[0].Comments[0];
if (!comment.IsReply)
 {
 comment.Reply(author, "Add Reply1", DateTime.Now);
 comment.Reply(author, "Add Reply2", DateTime.Now);
 }
ppt.Slides[0].DeleteComment(author, "Add Reply1");
ppt.SaveToFile(outputFile, FileFormat.Pptx2013);