As it turns out Microsoft has updated how EFS-encrypted files are displayed in Windows 10. Instead of green text, they are now displayed with a little yellow/golden lock icon overlay. Which is exactly what I see in the screen shot!
So, this is indeed a case of the files being encrypted with EFS. You’ll have the same problem probably opening the unencrypted PDF-files in the folder. This is not an AxCrypt problem, you’ll have to ask the person who mistakenly used EFS to encrypt the files to decrypt them.