Using MergeMultiplePdfsByCategory and getting error message saying appending PDF is encrypted but it is not encrypted

I'm using MergeMultiplePdfsByCategory and I'm getting an error message saying "Error: destination PDF is encrypted,  can't append encrypted PDF documents.".  None of the PDFs in the merge have been encrypted. I'm able to download and display the PDFs without using any passwords or decryption. Has anyone seen an issue like this? Any suggestions for how to approach a solution. Thanks in advance for your assistance.  
1 answers

This is a pdfbox issue. What did a simple google search yield? I get loads of hits for this issue, which of the proposed solutions have you tried yet?