Why doesn't Crownpeak allow me to edit the title of my PDF document?
Crownpeak does not control the PDF title. The PDF title is managed in the PDF itself. You will have to update the tile in the PDF itself by opening the document and going to File > Properties > Title.
Once the PDF title has been updated and the PDF has been published to the site, DQM will see the new title on the next schedule scan. It can take up to a week for that next schedule scan. If you have updated the title and the latest scan didn't pick up the new title then I would not remove it from the CMS and add it back. I would submit a case to Crownpeak support to have it reviewed. Let me know if that helps or if you have any other questions related to the PDF title.