DEVONthink Professional Doesn’t Recognize My Files
Like all Unix applications and many Mac OS X frameworks, DEVONthink Professional needs a file name extension to determine the file type of most files. Add the correct file name extension to your files (e.g. .txt for plain text files, .rtf for rich text files, .rtfd for rich text files with images, .pdf for PDFs and .doc for Microsoft Word files). Then try again.
Mac OS X normally saves files with the appended file type suffix, so this should not be a common problem.