'This file is damaged but is being repaired' after combining files with PdfFileEditor Concatenate

Hello,
I am combining multiple pdf files with the PdfFileEditor Concatenate function (memory stream array to single memory stream). See attached file for cut-down code.

The resulting pdf always brings up a message in Adobe Acrobat (reader or editor) that, 'This file is damaged but is being repaired'.

The file opens ok but there is always a request to save the repaired file on closing Acrobat. I want to avoid this request to save so need to create an 'undamaged' file.

At the moment I am just saving the byte array from PdfFileEditor Concatenate memstream output with a '.pdf' file extension. Do I need to finalize it somehow? I have tried creating a pdf document object from the memstream and then saving that but same problem.

Aspose pdf is version 9.5.0.0.


Thanks!