iText - Manipulate existing PDF - add dashes to end of each paragraph - itext

Question

I need to manipulate existing PDF in iText to add dashes to the end of each paragraph. Something like this:
I would make this in Word with tab leaders.
Is this possible to do with iText on an existing document.
Any help would be greatly appreciated.
Thanks!
Edit for clarifications
iText version is 5.5.x, but I guess we can upgrade it if the task would be easier with newer version.
There could be some paragraph that do not need dashes, but I have some control of the original PDF. It is assembled from different system and I could add some kind of markers to the paragraphs that need leaders (ie. I can add text like "~tab~" at the end of such paragraphs).
At the moment the documents that need this kind of editing have headers and footer, nothing but the text and one column with justified alignment.
Edit for even more clarification
I can even (by configuration) set where the dashes has to end (ie. at 10px) for specific document. We know every document type (and its structure) that needs to be manipulated this way.

Answer 1

This is insanely hard.
You should think of a PDF document as a container of instructions, rather than a WYSIWYG format. So finding out where lines are (let alone paragraphs) is very hard.
High level plan:
use IEventListener to process events from the PDF being parsed
look out for TextRenderInfo events, store them
sort TextRenderInfo events to ensure your list of events is in logical reading order.
merge items in your list if they appear on the same line and are less than a certain distance apart (for instance the distance of 3 spaces in the font specified by TextRenderInfo)
Now you should have lines
Merge lines if they appear in close vertical proximity of eachother and they overlap horizontally. How close they should be, and how much they overlap is something you'll have to figure out, and might differ from page to page, and document to document.
now you should have paragraphs
Figure out the bounding box of each paragraph. Or more accurately, the convex hull. There is a good algorithm for this called the gift-wrapping algorithm.
Now you can simply insert lines by inspecting your convex hull. This is the easy step.
If you can insert markers, you can easily do this using iText7. iText7 has an implementation of IEventListener that allows you to look for regular expressions within a PDF document. It returns the locations where the regular expression was found. If you can ensure your markers always satisfy some kind of regular expression, you can easily look for them, get their coordinates, and insert a line at the calculated position.
Of course, then you need to get rid of the marker text.
For that you can use pdfSweep.