What is the ruling on exchanging forms in a German company, where a form is sold for a certain amount and sent to the company for them to send three similar forms to be sold to others, with profits and prizes multiplying as the number of buyers increases, and with the possibility of extending the form's validity or changing the line to find buyers in case of no sale?

We understand from your question that the matter relates to filling out forms for a certain amount of money to obtain a larger sum through network marketing, and this is impermissible (haram (definition)) because it is a form of gambling (maysir (definition) and qimar). Even if there is a product, network marketing contains religious prohibitions such as uncertainty (gharar (definition)) and gambling (maysir).