I am try to find the entropy difference between encrypted and non-encrypted PDF files. In the various resources they find approximately non-encrypted entropy as about 7.70 and encrypted as 7.80 however I am calculating the encrypted entropy as 5.99. That means after the encryption the entropy of the PDF files is decreasing that contradicts with the resources. What it can be happened? Why my results are contradicts with the results of the resources?

Thank you for the answers, I have edited my questions.

It is a known fact that encrypting the files increases the file entropy. You can see the average entropy values of encrypted and non-encrypted versions of the different files in this paper (see figure 2). After I read this paper I check out my encryption algorithm and I notice that I was using base64 encoding while overwriting the file and that was decreasing the file entropy. So my problem is solved.