You could provide the readers of this forum with a minimum of information about the problem. So far, we know that "an adminstrator" seems to be unable to upload a pdf file to an animal, but "he has uploaded pdf files without a problem". We know that the upload percentage increases und that a "failed" message appears. We don't know anything about the sizes of the files involved, how large the percentage was when failing, whether other users can upload the same files to the same animal or other animals that the administrator can not. We don't know anything about the privileges associated with the administrator's account. We don't even have the answers to all questions I submitted above.
Some of the members in this forum know everything about there is to know about dokuwiki and then some. They can not help you without your giving a reasonable description of your incident.