java.io.IOException: Error: source PDF is encrypted, can't append encrypted PDF documents

In the release notes of PDFBox 2.0.0 RC2 we can read that (PDFBOX-1656) PDFMergerUtility is able to merge encrypted files. I have some files protected against modification with a password (users are allowed to open and print the file but its content is locked). I'm trying to merge those files into a single one but without success.

1. Adding source files.
2. Setting the destination filename.
3. Calling mergeDocuments().

Result is : Exception in thread "main" java.io.IOException: Error: source PDF is encrypted, can't append encrypted PDF documents.
at org.apache.pdfbox.multipdf.PDFMergerUtility.appendDocument(PDFMergerUtility.java:255)
at org.apache.pdfbox.multipdf.PDFMergerUtility.mergeDocuments(PDFMergerUtility.java:201)

Note : PDDocument.load() works if I need to print the files.
(Bonus Question : How could I decrypt a document before appending it to a new one (decrypt and openProtection are not used anymore))