Compare PDF Files

I need to compare two PDF files for additions/changes/deletions etc. (UPDATE: These PDF files are revisions of a tax return; as such, my goal is to share a comparison, not merge two text files.)

What have you used and recommend to “diff” PDFs?

This article identifies a few applications that can diff PDFs; do you have experience with any of them?

Thank you.

UPDATE 2022-02-04
Hoakley seems to think that it is not possible to do a good PDF diff

UPDATE 2022-02-05
Based on Daring Fireball’s suggestion of PDF Diff I bought the app and gave it a try. I found it unreliable for my purposes.

Look into – an app that has been around a long time and, when I’ve used earlier incarnations, was very impressive.


I neglected to fully describe my PDFs in the original post. My mother passed away last spring and I’m collaborating with several people via the internet to prepare her tax return. Thus, my need is to share the comparison, not merge two text files.

Thank you for the nudge to take a look at Kaleidoscope. I’d read a rave review of this app. But, I didn’t pursue it after looking at their website where they talk a lot about text files, a little about image files, and barely mention PDFs.

I downloaded a trial copy and put in my two tax return PDFs. Kaleidoscope does a great job of extracting the text from each PDF and making a comparison. At first glance it seems very complete. However, Kaleidoscope is not really designed for comparing PDFs, as it does not support graphic or pagination features:

  1. It doesn’t support checkboxes, which are very important in a tax return;
  2. It does not show page breaks or page numbers in either pane so it’s hard to trace the comparison panes back to the original PDFs; and
  3. It doesn’t provide any way to suppress comparisons of headers or footers so there is a lot of needless repetition in the differences

The killer problem, however, is that Kaleidoscope doesn’t appear to have any way of printing or exporting its comparison panes. Thus, I have no way to share the comparison with others. Yes, I tried just copying and pasting a into Word. And, yes this does capture the pane’s text. But it is just text with none of the color coding that indicates the changes.

I sent an email to their support people about printing or otherwise exporting the comparison information. Since neither Print nor Export are in the File menu, I’m not very optimistic that it can be done.

Now that my use case it better described, maybe you have another suggestion?

Thank you.

UPDATE 2022-02-06
Kaleidoscope confirms that there no way to output the comparison:

Currently there is no way to save/export/print a comparison, but that’s something we’ve been thinking about, too. So thanks for that feature request! For now, depending on the amount of change, a screenshot of the window might work? Not perfect, I know, but maybe a feasible workaround…

How about taking a screenshot of the comparison panes and then printing and/or exporting them?


Thank you for your suggestion to use a screenshot of one of the comparison panes.

Unfortunately, a screenshot is not good enough for two reasons:

  1. A screenshot is an image and I’d lose the ability to select/copy/paste the text. (No, I don’t have an Apple Silicon, e.g., M1, Mac so Monterey’s Live Text feature is not an option. I suppose that I could take a picture of the screen with my iPhone and convert the image to text there, but what a pain.)

  2. The text comparison is very long and it just isn’t practical to take this many screenshots.

What I’m really after is a “redlined” version of the PDF, much like Word provides for comparing .docx files.

I flirted with converting my PDFs into Word files and using Word to do the comparison. Unfortunately, my version of Word for Mac is very old—version 16—and does not support opening PDFs. Apparently the current version of Word for Mac (2021) does support opening PDFs.

At this point, my need for PDF comparison software has lapsed. The tax return revision review was completed the old-fashioned way, with printouts and eyeballs. Oh, how 20th century!

Nevertheless, I think there may be an unmet need for PDF comparison software (unless Word does a really good job of importing and comparing them).

Thank you again for your suggestion.

UPDATE 2022-02-17
I upgraded to Microsoft Office Home & Business for Mac 2021 with a perpetual license. Unfortunately, I’m not able to convert a PDF to an editable document using Word 2021 for Mac. See this post for details on my travails.

Apparently, Word (365, 2021, 2019, 2016, and 2013) for Windows can convert a PDF to an editable document locally, but I suspect that the only way Word 2021 for Mac can do so is to enable “Connected Experiences” so that it can be uploaded and converted on a Microsoft (?) server, just as was the case with Word 2016 for Mac.

I’m hesitant to upload a PDF with sensitive information to any server, even Microsoft’s. But at this point, I can’t even get a server-based conversion to work.

This won’t help with your comparison problem, but Live Text works on Intel Macs. And then there is also Text Sniper…

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You can download from the IRS a “Record of Account Transcript” for the last 3 years of income tax filings, including all amended returns. It is in a more condensed format than the original returns and has no checkboxes, so it should facilitate making comparisons. It’s a purely image PDF, so you have to OCR it.

For security purposes, I think the registration process includes their sending a confirmation code by postal mail to the taxpayer’s address on file. If that’s true, it won’t work if someone you don’t trust now lives at your mother’s address.

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I’ve not used it, but PDFMaster claims to be able to convert PDFs to all manner of other documents, so (in the future) you could use that and then do the file comparison in another app. I believe there’s a demo version so you could see how successful the conversion is:


Thank you for your suggestion.

Unfortunately, I’m trying to compare PDFs of drafts of a tax return before it is filed. So getting a transcript of a filed return doesn’t address my use case.


You are correct: both Live Text and Text Sniper work on all Intel-based Macs that can run Monterey, including my ancient “Late 2015” iMac. Apple expanded the supported hardware for Live Text in Monterey’s 4th beta during July 2021.

Thank you for pointing this out.

Thank you for suggesting a PDF → Word conversion application.

I took a look at Cisdem PDFMaster in Apple’s App Store. The ratings are sparse and all seven are between the dates of November 20-30. The November 20 rating was “1” and the following six ratings are 4-5 but I’m suspicious of them because of both the timing and the fact that several rater’s names are so similar; I wonder if these are fake users/ratings. The app’s version history goes back a year and having just six favorable (dubious) ratings does not give me much confidence in the app.

The free/demo version is limited to converting only 3 pages; upgrading to remove limitations for the PDF conversion features only costs $30. I downloaded the free version from the App Store and tried on one of my tax return PDFs.

The three-page conversion looks good. The formatting is a little off, but it’s good enough.

I will keep Cisdem PDFMaster in mind for future needs.

Thank you.

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I downloaded one of the Cisdem programs a few years ago, probably through a MacHeist bundle. It’s the OCR converter and it does work great, if you wanted a thumbs up for the company.



A free alternative, although I’m not sure how it will work in your particular case, is to Select All in each of the two PDFs to be compared and copy to separate BBEdit files, then use Search > Find Differences > Compare Two Front Windows. (This works in BBEdit free mode.)


Unfortunately, for my PDFs, the copied text is sometimes in a different order than it appears in the PDF. This makes it very difficult to know where exactly in the PDFs themselves any difference(s) occur. Worse still, sometimes the the order of copied text is different for each PDF, so you get false positive differences. Moreover, the labels for a series of cells occur separated from the data in the cells, making it very difficult to figure out which data corresponds to which line of the return.

I do like that the comparison panes scroll locked together; this is very nice.

Buy one month of Microsoft 365 for a few bucks.

As you can read in my “UPDATE 2022-02-17,” I can NOT get Word 2021 for Mac to convert a PDF to a editable document. I tried to do it from the online version of Word and also couldn’t do it there either. I don’t think that Microsoft 365 would give me any capabilities greater than Word online.

Using the 365 subscription service, I just opened a pdf file received over the internet and it opened as a “.doc” file fully editable.

Good to hear that Microsoft 365 for Mac is able to convert a PDF to an editable document.

And did the conversion happen on your local Mac or did it use “Connected Experience” to upload it to be converted?

I assume it’s an on-line conversion. When I just tried to open a PDF in Word, I was presented this dialog:

Screen Shot 2022-02-17 at 12.14.47

But the conversion seems to be limited to smaller documents. A 22 page Intel white paper converted fine. A 700 page book failed, as did a 1200-page ISO standard document.

Surprisingly, it was able to import a research paper set in two columns, and (mostly) preserved the layout.

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Yes! I think this is the dialog I clicked “Don’t Allow” on.

I can’t figure out how to get a chance to click on “Allow” now; do you have any ideas?

The dialog says: “Learn more about or turn off this service by going to Preferences > Security and Privacy.”

I presumed this refers to: Word → Preferences … (There is, of course, a “Security and Privacy” pane in  → System Preferences but I looked there and couldn’t find categories that look relevant to uploading a file for conversion.)

But, as you can see, there is only “Privacy” here, not “Security and Privacy” in Word → Preferences …

Clicking on Privacy brings up this:

I thought that “Manage Connected Experiences” would give me the opportunity to allow PDF uploads. Curiously, the “Learn More… “ link refers to a page that apparently applies to only Microsoft 365 products:

Excel for Microsoft 365 Word for Microsoft 365 Outlook for Microsoft 365 PowerPoint for Microsoft 365 Access for Microsoft 365 Publisher for Microsoft 365 Excel for Microsoft 365 for Mac Word for Microsoft 365 for Mac Outlook for Microsoft 365 for Mac PowerPoint for Microsoft 365 for Mac

As you can see, I’ve checked all the “Connected Experiences” checkboxes:

So …

Do you have any ideas how to get that dialog box you posted to appear again? How might I change my mind and now allow PDFs to be uploaded?

Thank you for taking the time to read this.

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