For outdenting text, you need to work with Paragraph.BulletOffset and Paragraph.TextOffset properties.
Below is the code, how to do it. Also see the output presentation which is attached with this post.
C#
Presentation pres = new Presentation();
Slide sld = pres.GetSlideByPosition(1);
Aspose.Slides.Rectangle rect = sld.Shapes.AddRectangle(100, 100, 3000, 2000);
rect.LineFormat.ShowLines = false;
TextFrame tf = rect.AddTextFrame("");
tf.WrapText = true;
//Normal paragraph
Paragraph para = tf.Paragraphs[0];
para.Text = "This is some text.";
//Create outdented paragraph
Paragraph newPara = new Paragraph(para);
newPara.Text = "This is some more text. This is some more text.";
newPara.Text += " This is some more text. This is some more text.";
newPara.BulletOffset = 200;
newPara.TextOffset = 200;
tf.Paragraphs.Add(newPara);
//Create another outdented paragraph
newPara = new Paragraph(para);
newPara.Text = "Another out dented text. Another out dented text.";
newPara.BulletOffset = 400;
newPara.TextOffset = 400;
tf.Paragraphs.Add(newPara);
//Create another outdented and bulleted paragraph
newPara = new Paragraph(para);
newPara.Text = "Another out dented and bulleted text. Another out dented and bulleted text.";
newPara.HasBullet = true;
newPara.BulletOffset = 400;
newPara.TextOffset = 600;
tf.Paragraphs.Add(newPara);
tf.FitShapeToText = true;
pres.Write("c:\\OutdentingText.ppt");