If slide has TextHolder you can change it but you can’t create new one. To add new text to a slide you should create Rectangle and add TextFrame to it.
1. Placeholder is a rectangular shape on a slide where some objects can be placed. They are read-only. 2. TextHolder is special type of Placeholder which contains text. 3. Shape - any shape on a slide. Each shape can contain TextFrame (sure, it can be null if shape doesn’t have any text). 4. TextFrame is text in a shape. 5. TextHolders and TextFrames have one or more Paragraph object. 6. Paragraph is part of text between carriage return characters. 7. Paragraph has one or more Portion objects. 8. Portion is set of characters with the same formatting.