Soon after starting your research work you should conclude on the Thesis Agreement together with your supervisor and the Dean of Studies. The Fachschaft Doktorat recommends to conclude on this as soon as possible because it is a safety measure for yourself.
The agreement is built up of three parts which are put together in one form. The three parts are described in the following. You can find the form on the homepages of the office of the dean (Dekanatszentrum) of your faculty. After filling in the form it should be signed by your supervisor and you. After this you should submit it in the office of the dean of your faculty. If you don't get any feedback or reply this means the it is approved by the Dean of Studis.
Link: https://www.tuwien.at/fileadmin/Assets/tu-wien/Organisation/universitaetsleitung/Dekanate/2016_11_10_TU_Wien_Dissertationsvereinbarung.pdf (we are aware that this form is provided separately by all faculties. We try to keep this link as up-to-date as possible)
The announcement of a doctoral thesis is mainly an information for the TU Wien that you are working on your thesis. As topic of your thesis you can choos a working title. This title is not necessarily the final topic of your dissertation. The announcement includes also a short abstract of your thesis.
The Thesis Agreement is an agreement between you and your supervisor. You should agree on how often you will have discussions about the dissertation progress. Since feedback is important for your research work the Fachschaft Doktorat recommends strongly to conclude as soon as possible on this after starting your research work.
In this part of the form the curricular part is defined. This means the courses within the curricular part (18 ECTS) are defined. If you want to or need to (e.g. when the course is not available anymore) change your courses after the approval by the Dean of Studies and your supervisor you should fill in a new appication and submit it in the office of the dean.