if I use
it shows me a disc as bullet. is it possible to change the symbol into a filled square? In Powerpoint it is possible to choose different symboles?
If this is not possible, is there any workaround for this? maybe choosing windings as font for the bullet?
Yes, you can set any other font for bullets (for example Symbol or Wingdings).
See Paragraph.setBulletFontIndex() function.
And change bullet character with Paragraph.setBulletCharacter()