Oh yes this can still happen when the pdf document isn't supported by PDF24 Creator. Sometimes there a some pdf documents which have wrong format, but adobe reader can still read the document because the program can handle some common errors in format.
The PDF24 Creator can't read encrypted documents too. The software can encrypt a pdf but after encryption the pdf can't be edited again. In this case a new pdf have to be created by printing this pdf on pdf24 pdf printer. This creates a pdf with same content in unencrypted format.
The pdf24 pdf creator is in continuous development so that the creator will support more special cases in future.