File Juicer can hide messages in images. An ordinary JPEG file can carry extra information like a PDF file attached to its end, and most applications will just treat it as an ordinary JPEG image.
This is not the same as encryption where you make it obvious that there is a secret message. An attached message can be read - if you know it is there.
To attach a PDF file on the end of a JPEG image follow this recipe
The JPEG which comes out of File Juicer can be emailed or put on a web site with its hidden load. You get the PDF out again by dropping the JPEG on File Juicer. You cannot edit it with any photo editing application and expect the secret attachment for be kept there.
Most file types can be used this way, except text files which cannot get attachments appended in this way. If you want to append a file type not directly supported by File Juicer, you can compress it with Finder to a zip file which File Juicer knows how to pull out.
You don't need File Juicer to append files this way. The Terminal has a built in command "cat" which does exactly the same thing.You enter the command:
cat photo.jpg message.pdf > enhancedphoto.jpgFile Juicer will extract files concatenated this way if it is any of the types mentioned in its Preferences.