[Answer]-How to create a preview of the documents and the ability to edit their content?

There is no django general algorithm for it.

django is python and therefore you can use common python code for opening and reading files. There are many examples of that if you just run google search.

After reading the file you can put out the contents of the file as a value for TextField in some form.

Just add script, that runs tinymce or some other wysiwyg editor script, to the mix and you have nice frontend for editing fields.

Alan