Comparing the 3 best pdf readers in Mac: Skim vs Highlights vs PDF expert

PDF files are the life of the academic. All information come with them. Of the time I spend reading, more than 95% of it goes by Pdf files. For that end, a good pdf reading application would be very important: much more important than any other application I use.

I have been looking for different tools for reading Pdf files.

Every one of them have strengths and weakness:

1. Skim

Skim: designed for the academic community: free and open source.


  • The ranked search is amazing.  of the  3, Skim has the best searching capabilities. PDF  expert comes next.
  • The annotations are more powerful and flexible: the anchored note is specially a wonderful tool. You can literally draft your next book using the anchored note. Reading triggers ideas; ideas breed ideas. Ideas cannot come out of the blue: they emerge during the reading. The best part of the anchored notes that you can give Titles to the notes. You can manipulate them so that the exported note will be much cooler.

I usually put ## on the title of the anchored note so that the title will come out as a true title when I exported the annotation using Markdown format.

  • The keep on top feature is very useful to compare ideas: any of the annotations can be kept on top.
  • Supports scripting
  • Export templates: you can modify these templates to your need. This is extremely useful.

But, there are some weaknesses with this all strength.

  • The non-standard format: if you want to read or see the annotations of the Skim, you have to export it. You cannot just open the pdf and keep on annotating. This is a deal breaker. Really. I am tied up to local system; this is like a prison. I like PDF expert for it adheres to the standard PDF specifications. I think it is the best mac reader with the standard formats next to Adobe’s own products.  Mac OS has this weird system comes by the name **PDFKit**: it gets broken, keep on screwing us all the time. Corporate greed seems the reason why we are suffering. Why doesn’t Apple adhere to the standard Adobe specifications? This same crap Kit also seems the  reason that saving pdf files in Preview and the rest of Mac local applications bulges up the size of the pdf.
  • The separate .SKIM file is a pain in the ass. It gets lost. If you export and import the pdf, all the annotations get duplicated. It is whole mess.

If Skim follows the standard PDF specifications; writing the annotations directly to the PDF itself, I would never look around.

2. Highlights


  •  It follows the standard annotation system: annotations made in Highlights can be viewed and edited in other editors (both in the mac and windows)
  • The annotations are powerful. The annotation panel could be wide: therefore,  a long text can be directly inserted. Even if it is not as convenient as the anchored notes in Skim, the panel is generally convenient to drop longish texts.
  • Works great with other applications: like Devonthink, Bookends, and Evernote. This is one of its best features
  • the exported notes are in Markdown format: this can be taken as strength and weakness: depending on your interests.
  • Splitting annotations into distinct notes. This is the most interesting feature, for me, because I can keep single ideas as separate notes. I  have been using Sente annotations for this purpose.


  • general clunkiness: the app contains a lot of bugs
  • the Splitting feature is not well worked out. I would have bought this app if I were able to assign titles to each of the annotations. The Titles are very useful for summarizing the concepts of each of the singular annotations. This is the most debilitating problem I have with Highlights. The spliced notes have no meaning: not life because they are not customized by titles or tags.

3. PDF expert

PDF expert is very fast and fluid application. I use it everyday. The developers are generally very responsible and fast guys. The code they write is amazing. The programmer talent in Readdle  tend to be very high. I participated in their beta versions for a long time now. I can tell you, their betas are more matured and reliable than the final releases that Apple sends out. There are some small details: specially its speed, which makes this app worth trying. I like it so much. I is the first app I open in the morning. The best part of the app is that it follows the standard Adobe system. The annotations made in PDF expert are visible on any other pdf reader. That is why I use it as my default reader.


  • I also like the new searching tool. It searches all the open files.
  • it automatically detects the true pages numbers of the pdf
  • blazing fast
  • follows the standard Acrobat annotation format
  • The annotation tools are generally ok

Unfortunately, PDF expert is also  the least creative of the 3 apps I am trying. The features it contain are most already in acrobat or other pdf readers.  The export features are very weak: even terrible. I tried to export in the Markdown format. It doesn’t permit me to customize on what types of text I want to export. Generally, the exported text turn out to be  vary bad containing unwanted stuff (like Date, author…).  Even if there is wondrous programming talent,  the direction they are taking are mundane and non-creative.There is barely a new feature in this reader that other readers, like PDFPen, Acrobat etc, do not have.   They don’t understand the areas of need. The annotation tools could  be better. The developers of Highlights have truly understood the needs of the scientific community.  It is only the implementation that is lacking in the latter.

My take:

After trying it on a couple of times, I have given up with highlights.

I am now using Pdf expert and Skim. I use Pdf expert for fast reading. When I have to just scan and take a few points, I open my file with it. I highlight a bit; clip a few lines to Curiota and close it down.

When I have to read a book or an article from the beginning to the end, for intensive reading, no reader offers the comfort that Skim offers. The exports are also much robust. Therefore, for in-depth reading, I am relying on Skim.

By the way, there is an other candidate that could offer a similar comfort for reading: the Marginnote. It seems to have some great annotation tools similar to anchored note: even better, mind mapping within the reader. I tried it for a couple of minutes. But, I dropped the app immediately because the annotations are in proprietary format: they will be a big lock down. While the annotation summary can be exported, the annotation and the annotated pdf are divorced forever. I am skeptic of apps that highly rely with proprietary file system.