How to create "Custom Forms" that trigger own business-logic / do not create any Content I'm new to Drupal, so sorry for this maybe simple question.

I'd like to create some kind of content-type, which a user can "create" and fill the forms, but instead of just saving the content to the database, i want Drupal to pass the values to a 3rd party software (which can be accessed by socket-communication), wich renders PDF's from the text the user entered.

The PDF should be displayed to the user after Form submission.

I know, i can use Drupal to render PDFs, but i want to connect to our legacy 3rd Party software.

So the question is: How and where can i hook-in to write my custom 3rd-Party socket-communication-phpcode and display the result to the user (or save it to drupal db, or, or, )?! 

Thanks in advance!
Create your form by using the drupa FAPI.
Set-up a path to your form using hook_menu.
Call your custom communicatin code from your FAPI submit handler.