Password Protected Files Silenty Skipped in Merge

I want to loop through a large set of PDF files merging them all into one new file. Some of the PDFs may be password-protected, but this is not something I know upfront. I'm using LoadFromFile with the PDF file names and passing in a blank string for the password. On password-protected files, I noticed that no error occurs when I call LoadFromFile with no password and then call MergeDocument and pass in the PDF to merge. Instead the pages for that PDF just get skipped altogether and do not appear in my output. In other PDF libraries I've used, trying to access the document data without the password would trigger an exception so these cases can be identified. What are my options if I want to use this PDF library but can have situations like this with unknown password-protected files? Is there a way to identify when the content can't get retrieved because the proper password was not used when loading the document?