just like How can I superimpose LaTeX / TeX output over a PDF file? except I want to write over a multi-page text file, brought into my main .tex file with:
\newgeometry{left=3mm,right=5mm}
VerbatimInput{}
\restoregeometry
from Include data from a .txt verbatim . Additionally, due to the text file, I also wrapped a margin changer.
If I can write on top of this text with absolute positioning I can't image the margins being a problem.
Other than writing on top of pdfs, or forcing figures on top of each other, I did not see anything useful (at least that I could understand).
Lastly, I would like to write in a different color, but I guess I could just do something like
{\color{blue}{text here}}
I didn't provide a MWE because my data file I would like to write upon is long but not really important, and the two links I provided should suffice... I hope!
P.S. I should note that I can get things like this: How can I set the position of text along path in tikz more precisely? to work - text on a tikz path, but I'm unsure how to do such things, positioned absolutely, for a specific page in a multi-page text file from VerbatimInput. Also, I don't need a path, just normal text...
P.P.S. I guess what an equivalent thing I would like is something like this.
\begin{verbatim}
copy and pasted text from data file
\end{verbatim}
...at this line, the reason for the above text in the text file is...
\begin{verbatim}
continuing copy and paste of data file
\end{verbatim}
...another comment about something in the data file, probably in color
\begin{verbatim}
rest of copy and paste of data file
\end{verbatim}
The only problem, which is minor, is that it makes my .tex file long and hard to naviage.

listingspackage, you can define which lines are included in your text, so you can include comments as regular text between fragments of verbatim code. – Ignasi Dec 09 '15 at 16:29