(Illustration by Traci Daberko)

If there is one type of mobile app that has truly earned its keep with lawyers, it is the PDF reader/annotator. Lawyers have no shortage of documents to mark up, and tablets, with their touch interfaces and easy adaptability to stylus-based (or finger-based) writing, make an ideal platform on which to do so. Over the years, an array of PDF apps have taken the field, the best of them pulling off that all-too-rare feat in the tablet world: They do what they say they will do.

The big names in this category are pretty consistent from year to year, but they’ve been steadily tweaked by their makers, gaining new features and improvements. With the recent release of an upgraded GoodReader, a perennial attorney favorite, this is a good time to look at the latest incarnations of three top iPad PDF apps. (One of them, iAnnotate, is also available on Android, though with a more limited feature set.) You can’t go wrong with any of these apps, but depending on your needs, you may go further with one of them than the others.

GoodReader 4. The latest version of this app isn’t a free update for existing owners, as all previous enhancements had been. It’s a $6.99 purchase, no matter how far you and GoodReader go back. While such a pricing strategy often creates controversy, GoodReader has fared just fine, with the app still a fixture on Apple’s Top 100 chart. There’s good reason for that: GoodReader’s feature set has long been almost overwhelming, and this latest version brings even more bells and whistles.

I liked two enhancements in particular. First, you can email individual pages within a PDF—a seemingly obvious but rarely found feature. Second, there is a new scrollbar appearing on the bottom of the screen. Not only does it let you move quickly within a large PDF, it displays thumbnails of each page as you scroll, making it even easier to get to the right place.

Other new features, like the ability to add pages to a PDF and delete and rearrange pages, are nice too. Search is implemented particularly well, though the search button isn’t as prominent as it should be (I had to hunt for it). GoodReader not only lets you move through all instances of a search term but provides a handy back button to immediately return you to where you started, no matter how far into the search you’ve gone. It’s another feature PDF apps often lack.

GoodReader has long been a champ when it comes to file management, a capability that has never been one of the iPad’s strong points. Once you have downloaded your PDF into GoodReader’s local storage—easy to do via email attachments, the app’s built-in Web browser, or syncing with Dropbox or another of the supported cloud-based services—it’s a snap to create folders (say, for individual clients or cases) and move files between them. And each of those files can be protected with a password—another useful feature that many apps don’t provide.

All that functionality comes at a cost: GoodReader is not the most intuitive application and the interface would benefit from a bit more streamlining. There is a kitchen sink of features here, and GoodReader will never let you forget that. But learning its many ins and outs is time well spent—and for many lawyers, an effort that will be rewarded. (GoodReader 4, Good.iWare Ltd., $6.99)

• iAnnotate PDF. While iAnnotate doesn’t quite match GoodReader’s breadth of features, for many users that will be its selling point. This $9.99 app’s interface is deceptively simple. Smartly designed menus, each covering a core task like annotation, navigation and file management, can be pulled out when needed from the edges of the screen. The result is a lot of functionality with a minimum of clutter. As is the case with GoodReader, you can scroll through thumbnails of each PDF page, though you can’t email individual pages.

For lawyers, the feature that may set iAnnotate apart is the ability to mark up Microsoft Word documents and PowerPoint decks. What you are really marking up is a PDF of your file, but iAnnotate does the converting for you. (Other applications make you do the conversion yourself, using software outside of their app.) The catch here is that you need to be connected to the Internet when you first open the Word or PowerPoint file, since the conversion is performed on a server maintained by iAnnotate’s maker, Branchfire Inc. It’s not a big deal, but it does require planning ahead if you’re going to be off the grid.

Like the other PDF apps reviewed here, iAnnotate lets you create folders and move files between them. You can also download PDFs directly via the app’s built-in Web browser. One gripe I had was how iAnnotate downloads files into whichever folder you were most recently working with. If you tend to move back and forth among folders, it could be a bit of hassle to figure out where recent files were saved. A better option would be to have a central download folder.

But this is a minor quibble. With its clean interface, Word-to-PDF conversion, and ample-enough annotation tools, iAnnotate is both accessible and capable. For many users, that will be a compelling combination. (​iAnnotate, Branchfire 
Inc., $9.99)

PDF Expert 5. Like GoodReader 4, the latest version of PDF Expert is a paid upgrade, meaning that owners of previous versions will need to pay same $9.99 as those who have never used the software. For that ten-spot, though, you get a lot.

For one thing, PDF Expert sports the most attractive interface of the bunch. It has a clutter-free design and makes good use of colors and icons to draw your eye to features and files. When tapped, prominently placed buttons for annotation, search, file management and other functions trigger the related menus, so you get a wealth of features without being overwhelmed. (I’m looking at you, GoodReader.) Another slick touch: You can drag and drop files into user-created folders. And, as with GoodReader, you can email individual PDF pages.

But I found that the app’s good looks masked some clunkiness. Not all tasks are intuitive. For example, changing the color of a highlighter pen requires you to tap and hold the highlighter icon to bring up the color palette. Nor is there a built-in browser with which to grab PDFs off the Internet. Instead, you need to go outside the app and use your tablet’s browser. (On the upside, PDF Expert lets you choose, and change, the directory that it uses to store downloads.) Unlike GoodReader, PDF Expert doesn’t allow you to password-protect individual PDFs—you can only set a password for the app itself.

While PDF Expert’s developers like to tout its handling of forms (you can add text, check boxes, and select items from drop-down lists), the app’s “Review Mode” will probably be of more interest to lawyers. That feature lets you mark up PDFs in a way similar to Microsoft Office’s Track Changes. Instead of writing notes in the margins or drawing angry red circles around offending passages, you can made changes directly in the text via an on-screen keyboard or an add-on keyboard, if you have one. Deleted text is marked with strike-throughs and new copy is appended. The result is a mark-up that is easy for recipients to follow. The modifications are saved as so-called smart annotations: They don’t change the underlying text of the PDF, so you can always go back to the original. And if you get nostalgic for those margin notes and angry red circles, you can still add them, via the app’s annotation tools.

These three apps are top-quality,
and I liked all of them. My personal preference is for GoodReader, but that’s mainly because I’m past that app’s learning curve. I can certainly see other users opting for one of its rivals, particularly if they needed one of the features unique to those apps. It’s great to see a category that really shows off, and helps lawyers realize, the potential of tablets. Now we just need to see more of them. (PDF Expert 5, Readdle, $9.99)

Contributing editor Alan Cohen writes about law firms and technology.