PDF annotation app suitable for a proofreader?

Can anyone suggest a non-Adobe app that makes it easy to proofread and mark up long documents?

I know there are endless web discussions about the merits of different PDF readers and editors, including on this fine forum. But mine is a fairly specific request, and perhaps one of you can advise.

So … I’d like to be able to highlight a word or sentence in the text, and attach an associated change or comment so that it shows up in a sidebar or a popover. If I have to change between tools then there needs to be keyboard shortcuts, and the resulting markup has to work in the Windows world.

The free version of Acrobat used to do this pretty well, at least when it was called (IIRC) Adobe Reader DC. The current version of Adobe Acrobat Reader can still associate a comment with a highlight, and has other useful markup tools like “insert text”. But there no longer seems to be an easy way to change between tools, and the app is a memory hog that often brings my M1 mini to a halt.

(The full version of Acrobat may well do better, but I’m not willing to pay for it.)

My favourite PDF Expert can highlight and add notes, but it can’t associate a note with a highlight or any other kind of anchor in the text. I need to be able to attach a comment or instruction to a single letter or comma, and I don’t find standard PDF notes very accurate for that. Using both a highlight and a note is clumsy and makes life harder for whoever is correcting the original file.

Preview.app is much the same. Nitro PDF Pro is expensive but I’d probably cough up if it has decent markup tools. However, I can’t even work out how to download the trial version – the form they refer to doesn’t show on my screen.

In MS Word this is a trivial job using comments or change tracking. Why is it so complicated for PDFs?

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Not only Word. Google docs can do this beautifully and since our entire campus is a Google shop I end up using that a lot. It always bothered me that Preview can’t do the same great markup job for a PDF. I’m afraid I don’t have any good tips for you as to PDF apps, but I’m very curious what others suggest for this specific use case.

That looks like a Safari issue. The form doesn’t display in Safari (Sonoma) on my Mac either, but it works fine in Firefox and Chrome/Edge.

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I’ve long been in the same situation (marking up student papers) and now I import them into Word and use the features there. I leave them as docx but you could import, make the comments, and then send them back to PDF – I think. I haven’t tried it.

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Yo can try Liquid Text…

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Thanks for making me persevere. I’d already tried Brave and that didn’t work. I think it was probably my Pi-Hole, but even after disabling that it was still a struggle.

Anyway: I conclude that Nitro PDF is still as ugly as in the days of PDF Pen Pro, and more to the point it won’t attach a text note to a highlight or a text selection. I was excited to see the “Comment” tool, but that turns out to be just a text annotation with a border.

I’m wondering whether most of these apps just use whatever functions are provided by PDFKit, while Adobe goes a step further.

Thank you! I did, and their “Comment” tool is quite neat, though I think they could do a better job of showing the link back to the related text.

I’m not totally convinced about the PDF export, which is needed to collaborate with the rest of the world, and it’s a super-ugly non-native app. But it’s good to see some new thinking. I’ll try it for a while.

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@Simon and @silbey thank you both for your comments. Glad to hear I’m not alone. I think converting to docx may be the answer.

I’ve previously avoided this because I found that the converted files often depended on Word’s text boxes to achieve a layout that’s somewhat faithful to the original PDF. If you ever use macros to clean up Word documents you’ll know that text boxes add a load of complexity and there’s a risk of missing some of the text.

But I’ve just tried Nitro’s online converter on a fairly complex layout (a 70-page company annual report) and it did a really good job without using text boxes, as far as I can see.

The resulting Word file isn’t exactly easy on the eye, but the text flow is loads better than what I get by simply copying and pasting the PDF text. It might even be possible to simplify it automatically, perhaps by removing column and page breaks. So thanks again for the whole idea.


PDF = a bag of hurt, unfortunately.

Both in terms of per app edits/markup functionality differences, along with other apps viewability of said app’s edits/markups afterwards. And yes, Adobe Acrobat Pro (Mac users have to buy the Pro version, at the stupidly high price ~$£€240 per YEAR!) tends to hold the title for ‘per standards’ reliability, although even that’s not totally reliable when opened/read/re-edited in other apps.


I have nothing to suggest, sorry. But I do have questions.

As someone who worked with 8 inch floppy disks, I have never gotten over being concerned about file size. What does editing a PDF do to the file size? (And while I’m interested in the answer, I also welcome gentle observations that no one realistically worries about file size any more, if that’s true.)

In a recent interaction with a business, my responses were reported on four different screens. I saved each to a PDF; they are 38 KB, 42 KB, 64 KB, and 38 KB in size. I used Preview to combine them into one PDF; it is 485 KB. Why? What can I do about it?

I would expect editing a PDF would result in similar bloat. Is that ever an issue?


One of the challenges with PDFs is that there are multiple ways to generate files that produce the same visual/printed output. Different apps may have different approaches to the challenges, and each of these ways has its own efficiency with respect to file size, memory consumption, and so on.

One possibility in the example you mentioned is that the original PDFs did not include an embedded font, while your combined file did, but that’s just speculation on my part.

FWIW, many PDF editors have “pre-flight” tools or settings that can shrink file sizes significantly, with or without compromising output quality. For example, they might remove hidden content, flatten empty layers, or downsize the resolution of bitmapped images. These tools/settings can be complicated to master, unfortunately.

Personally, I often use Apago PDF Shrink to reduce the size of my PDFs. It’s easy to use, and it has a selection of pre-set defaults work well for me, though they may not be optimal for everyone.

+1 for Apago’s PDF Shrink. I note that there’s a different (and cheaper) app with the same name in the App Store, which I can’t vouch for.

I’m sure there was a discussion here about PDF shrinking recently, but I can’t find it.


If you are working on a project with a publisher or a company that has access to their own copy of Adobe Acrobat Pro, they can can post a copy of the PDF to be edited on their web site and give you access to the document there for editing and proofreading. I have done it for magazine articles, and it’s it works very well. This feature was added in the last year or two, and some editors do not know it exists. Publishers like this because the alternative for many writers who don’t own/can’t afford the full Acrobat is to print out a copy and edit on paper.

I recently had to work Change Tracking on Google Docs and found what I consider a fatal flaw. It does not pin changes to their location in the document, so I was not able to tell where the changes belonged when I imported the file into MS Word. I have never found a word processor I could trust to replicate change tracking MS Word without introducing problems in a project I was getting paid for.


Skim is a good app for annotating PDFs and has all the features you need. It has several annotation options:

And the Anchored Note type allows choosing an appropriate icon:

For the Highlight annotation type, by default the entry in the sidebar is titled with the text you have highlighted (first sidebar entry in the screenshot below). But you can double click to edit the title in the sidebar and change it to a comment (second (highlighted) sidebar entry below) so you have a suggested edit attached to the specific highlighted text.

Keyboard shortcuts are great, including some single-key ones to switch between annotation tools (e.g. H for the highlighter, B for the box, etc). See the Hidden Shortcuts section of the wiki, or press ? to show them all.

The one thing I don’t know is how the annotations will show in PDF readers on Windows. You will definitely need to use the export with embedded notes feature of Skim, as its native file format uses extended attributes to store the annotations. But if I export with embedded notes, Preview shows the annotations properly, so I assume Skim is using the appropriate PDF standards to embed the annotations.


@jzw Thanks so much for this excellent tutorial. I’ve had Skim installed for years, but never used it properly, and for this purpose I didn’t think it would work. Howard Oakley I think says that Skim does annotations “correctly” – the extended attributes thing – which is to say it’s out of sync with the rest of the Mac PDF world.

But your reference to exporting with embedded notes sounds as if that issue can be worked around. If the annotations show up in Preview, we should be OK. I will investigate.


I really like the way Skim does it. Once I finally discovered where the notes sidebar lives (and how to make it visible!) and how an anchored note works (I’d love to highlight and anchor in one), I was feeling pretty great.

Until I opened a PDF that somebody else had edited in some Windows PDF tool (perhaps Acrobat, no idea). Their notes displayed with the same teeny tiny icon Preview uses and worse yet, none of their notes showed in the notes sidebar. Would be nice if Skim could somehow display poorly done annotation in the same way as its IMHO superior method.

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Can Skim combine PDFs? I could not find the answer to that question in the FAQ or other parts of the web site.

I don’t think so. I use Preview for that.


Not to answer this directly, but I’ve just discovered the command-line tool mutool, which is a component of MuPDF (available via Homebrew). It can combine PDFs in interesting ways, such as with comma-separated lists of page ranges.

I’ve used it to split PDFs that were created as printer’s spreads into individual pages. The job that prompted my original post involved a PDF with spreads and small print, which required a lot of sideways scrolling. Splitting the pages in half vertically made it easier to view.

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I’ve used Preview for marking up PDFs but nothing as complex as proofreading a manuscript. For that I’ve always used Word. I submit a Word manuscript and the editor or copy editor returns the marked up file. I’ve never seen a PDF app with that level of granularity.

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