Is it somehow possible to extend my PDF sheet depending on how many fields need to be visible.
Lets say I have a pdf file 10 x 20 cm. I got 5 textfields thats fit into this sheet. I can activate a 6th textfield with a checkbox. But there is no more space for the textfield. So the sheet sould extend for another whole new sheet if I activate the 6th textfield.
As per your description above, we understand that you wish that if a new field is added, the PDF sheet should adjust its size accordingly. So, all 6 form fields appear on a single sheet. I am afraid to say that, by default, it is not possible.
However, it may be achieved by a workaround. If you are creating a PDF form from other format files, you may reduce the text size to adjust the field on the same page.
You may also try changing text size using the Edit PDF tool, however, it may not be the ideal way.
Could you please let us know how exactly you are creating the PDF? It will help us to provide you with the right steps or suggestions for that.