You can read directly in jPreTeX a LaTeX file, and modify it easily.
In order to do this, click on "Open a Document" button : a dialog box opens.
Then choose in the combo box "Files of type" the "TeX Files" item.
You have all the TeX files contained in the current directory. You can navigate among the directories.
Then choose the file you are interested in. jPreTeX converts it in a jPreTeX document, adding "bis" to its name.
Of course the conversion may not be perfect, but this can allow you to work with colleagues not having jPreTeX !