What you see is not what you get in the PDF document format

The sharing and storage of scientific knowledge, information and data are today mainly in digitized form, which will become the predominant means of communicating scientific work in the future. One of the best-established formats is the open standard of PDF (Portable Document Format), which is renowned for its flexibility and stability. In this article, we expose a major flaw in the format with respect to the security of confidential information, such that even organizations responsible for safeguarding and setting the standards for data management were unintentionally revealing confidential patient data. By collecting and analysing a random sample of files from a health informatics organization, we demonstrate the extent of the problem and determine its cause by code analysis of an example. In conclusion, we suggest the development of a knowledge-sharing format that does not demand expert skills for safe usage: WYSIWYS (What You See Is What You Store).