@Hessel Wellema Thanks for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this.
Based on the shared information, I understand that you want to create an index in azure search service and to upload an PDF document in it using the Rest API.
If my understanding is correct, then you can go through this documentation on how to create the index using Rest API.
Hope this helps, let me know if you have any further questions on this.