If you have other formats like word or pages, use those programs to save the files to .txt or .rtf and import.
PDF files are funny things. They may look like text when you are viewing them, but actually they may be images or other objects and they can be difficult to get the text from.
There are 5 type of filter to use on the PDF to extract text whatever the format.
In a perfect world the Document type would be used to get the text. If this does not give you all the text, try one of the other options.
