Can I add inline or margin comments to the pdf?

Yes, you can use the todonotes package (covered here) or read our help page on margin notes, which discusses the \marginpar command and the marginnote package.

Loading the todonotes package

To use the todonotes package, add the following line to your document preamble: 

\usepackage[colorinlistoftodos]{todonotes}

The colorinlistoftodos option adds small coloured squares to the list of todo notes (see below), helping to distinguish between different types.

  • Note: Readers are strongly encouraged to browse the todonotes documentation for information on package options, valuable commands and helpful examples.

Use the following command to add a comment: 

\todo{This is a comment that will appear in the margin}

Example using the todonotes package

Below is a basic example to help you get started: it demonstrates various note styles and produces a list of todo notes via the command 

\listoftodos[Title of your list...]

which takes an optional argument, enclosed in [...], used to typeset a title for the list of notes. 

\documentclass[a4paper]{article}
\usepackage[colorlinks]{hyperref}
\usepackage[colorinlistoftodos]{todonotes}
\begin{document}
\listoftodos[A list of things I need to finish]

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Nulla
\todo{Plain todonotes.} urna. Maecenas interdum nunc in augue. 
Mauris quis massa in ante tincidunt mollis. Proin imperdiet. 
Donec porttitor pede id est. Sed in ante. Integer id arcu. Nam 
lectus nisl, posuere sit amet, imperdiet ut, tristique ac, lorem. 
In erat. In commodo enim. \todo[color=blue!40]{Todonote with a different color.}%
Phasellus libero ipsum, tempor a, pharetra consequat, pellentesque
sit amet, sem. Praesent ut augue luctus elit adipiscing ultricies.
Vestibulum suscipit cursus leo. Nullam molestie justo.

Morbi dui. Morbi convallis mi sed sem. Nulla convallis lacus vitae
risus. Phasellus adipiscing. Nullam tortor. Sed laoreet aliquam
ante. Vestibulum diam. Pellentesque nec leo. Pellentesque velit.
\todo[nolist]{Todonote that is only shown in the margin and not in
the list of todos.}%
Praesent congue mi eu ipsum cursus fringilla. Etiam leo erat,
tristique et, pharetra eget, mollis vitae, velit. In hac habitasse
\todo[size=\small, color=green!40]{A note with a small fontsize.}%
platea dictumst. In quam nibh, facilisis et, laoreet non, facilisis
tempus, justo. Class aptent taciti sociosqu ad litora torquent per
conubia nostra, per inceptos himenaeos.

\todo[inline]{testing testing}

Donec nulla lectus, faucibus sit amet, auctor non, consectetuer
quis, pede. Nullam dictum. Nullam suscipit, ligula in scelerisque
\todo[noline]{A note with no line back to the text.}%
posuere, sapien purus rutrum magna, vitae pharetra leo quam vel
tortor. Donec eleifend condimentum sapien. Etiam sed orci. Aliquam
\todo[inline, color=red!50]{Inline todonotes.}%
tempor. Pellentesque egestas tortor id eros. Donec mauris justo,
commodo id, pellentesque id, eleifend non, mi. Duis venenatis
sagittis metus. Donec tempus metus id lacus. Praesent vel diam.
Morbi nec ante. Vestibulum varius felis ac lacus. Nulla vitae neque
\todo[inline, color=green!40]{A note with no line back to the text.}%
in nibh bibendum volutpat. Quisque accumsan diam. Aenean ultricies
nisl ac lacus. Aliquam posuere. Aenean venenatis tortor in felis.
\end{document}

 Open this example in Overleaf

This example produces the following output:

Demonstrating the todonotes package on Overleaf

Further reading

Overleaf guides

LaTeX Basics

Mathematics

Figures and tables

References and Citations

Languages

Document structure

Formatting

Fonts

Presentations

Commands

Field specific

Class files

Advanced TeX/LaTeX