According to the calibre user manual PDF is one of the output formats supported by calibre. To do this start calibre and use the Add Books menu and the 'Add books from a single directory' menu item to add the cbr file to calibre. Then select the cbr file in calibre and use the Convert Books menu and the 'Convert individually' menu item. When the convert dialog box is displayed, in the top right hand corner select PDF as the output format. Click the OK button and the conversion will begin. The lower right part of the calibre screen will show that the conversion has been assigned a job and is underway.