There are lots of apps that can work with PDF files on the iPad and iPhone, but PDFpen by Smile Software is one that I frequently recommend because it has a nice set of features and is easy to use. I have reviewed both PDFpen for iPad and PDFpen for iPhone. About two months ago, Smile Software came out with PDFpen Scan+, an app that can scan a document using the iPhone's camera, create a PDF file, and perform OCR (Optical Character Recognition) to recognize the words in the document and thus create a readable PDF file. Readable PDF files are far better than PDF files that simply contain an image of the document because you can search for words in readable PDF files and you can more easily highlight and otherwise annotate the text.
I bought PDFpen Scan+, a $4.99 app, and I have been using it whenever I have a need to scan a document on my iPhone — a need that I don't have very often, but when I do it is nice to have a good app. After using this app from time to time over the past two months, I'm not very impressed with the app as a scanner, but it I love the OCR feature, not only becuase it is usually quite accurate but also because the OCR occurs right on the iPhone itself without sending my document to some third party who I do not know or trust.
You can always take a picture of a document using the iPhone with the built-in Camera app, and there are quite a few apps that go one step farther and let you save the scanned image(s) as a PDF document, making it easier to work with and share the file. For over a year now, my favorite app for scanning a document has been Scanner Pro by Readdle.
PDFpen Scan+ works okay as a scanner, but it is not as good as Scanner Pro for two reasons. First, an iPhone scanner program needs to have a good way to find the four corners of the document to straighten the image since you will rarely be lucky enough to hold your iPhone directly on top of a document 100% parallel to the document itself. PDFpen Scan + automatically tries to find the edges and four corners of a document after it takes a picture, and it does a decent job, but if you want to make adjustments it is difficult to do so. You make adjustments by dragging blue dots to each of the four corners of the document, but because your finger is on top of the dot when you are dragging, your finger makes it difficult to find the exact edges of the document, often resulting in frustrating experience. [UPDATE 5/8/14: The latest version of PDFpen Scan+ has completely changed how the app handles page edges, and addresses all of my concerns. See this video from David Sparks to see the new version of the app in action.]
Scanner Pro has two solutions for the can't-see-under-your-finger problem. First, when you are holding your iPhone over the document and before you even press the button to take the picture, the app already starts trying to find the edges of the document and shows you what it is doing on screen. Thus, you can tilt your iPhone until the app best sees all edges and corners of the document before you take your picture. Second, if you have to make further adjustments (and it is rare that you need to do so), Scanner Pro displays a circle with a zoomed image of what is under your finger and places the circle far from your finger so that your finger is not covering it up, making it easy to move the blue dot to the exact corner of the document. The following two images show Scanner Plus in action, and I wish that PDFpen Scan+ worked the same way:
My second complaint about PDFpen Scan+ as a scanner is that the quality of the image is not great. On the plus side, it gives you the option of converting your document to pure black-and-white, which typically results in a far better image and can often compensate for your any uneven lighting of your document. But even in black and white mode, the quality of the image resembles something that you might expect from a fax machine. In the following two images, I'm showing a close-up part of the same document, first scanned in PDFpen Scan+ and second scanned in Scanner Pro:
The difference in quality is obvious to the eye, but is confirmed by the file size (although a larger size is not always synonymous with a better image). PDF files created by PDFpen Scan+ are about a third of the size of PDF files created by Scanner Pro.
So overall, PDFpen Scan+ does just an okay job with scanning a document, and I prefer to use Scanner Pro.
OCR'ing a document
What sets PDFpen Scan+ apart from Scanner Pro and most other iPhone document scanners is that PDFpen Scan+ can OCR the text in an image and create a readable PDF file. And unlike some apps like ABBYY FineReader Touch that accomplish this by sending the document off to a service on the Internet and then downloading the document later, PDFpen Scan+ performs the OCR right on the iPhone itself. I like this approach much better because it is faster and it is more secure. If I am scanning a confidential document, I don't want it sent off to some computer owned by a third party to have the text in the document read by a machine that isn't under my control.
The process of creating an OCR version of a document is simple. Just select the document and tap the OCR button. You can actually "see" the app working because yellow lines go down the screen as it scans each line of text — a fun animation that is also useful keeping tabs on the process.
Once the OCR process is complete, you then have two options. First, you can copy the text of the document to the clipboard, useful if you want to paste it into a word processing document or an email. In the first image below, I pasted the text into the iPhone's Notes app, which shows you that the quality of the OCR with a good original is excellent. In this example, the only error in the entire document was on the RE: line of the correspondence; the original said "Doe v. Jones" and PDFpen instead read "|_)oe v" and didn't see the "Jones" part at all. It's not perfect, but I never expect OCR to be perfect even on a computer, let alone on an iPhone.
The second option is to share the readable PDF file. You can email the document, open it in another app on your iPhone, or export it to a cloud storage service such as Dropbox. Every option I would ever want is in there.
The best part of the OCR function of PDFpen Scan+ is that you aren't limited to using it with scans created by the app. I noted above that Scanner Pro creates better scans then PDFpen Scan+, but Scanner Pro doesn't have an OCR function. What I've been doing over the last few months is scan the document with Scanner Pro, then send that PDF file to PDFpen Scan+, and then OCR the file using PDFpen Scan+. The result is the best of both worlds — a higher quality document that is readable thanks to the OCR process.
Moreover, I've had other attorneys send me non-readable PDF documents — PDF files that simply contain an image of the document. I use PDFpen Scan+ to create a readable version of the document so that I can search through the document to find the part of the document that uses a specific word. And if I want to highlight a document, this is far easier to do when you are working with a readable PDF file.
OCR works best with a simple document such as a letter with black text on a white background. If the image quality is poor, or if you have a complicated document such as one with two columns of text, the app misses words or misreads words. In my real world tests, the documents that I have worked with in my law practice have been of good enough quality for PDFpen Scan+ to give me great results, even though accuracy is not always 100%.
Do note that the results are not as good as what you can get on your computer using software that can perform OCR. First, scanning documents on an iPhone or iPad is slower. Second, when PDFpen Scan+ creates a readable PDF file, it vastly increases the file size. I've seen 45 KB PDF files become 500 KB PDF files after this app performs OCR. Third, although the quality of the OCR is quite good, I get better results using software on my computer such as Adobe Acrobat Pro or Nuance PDF Converter. On the other hand, I love the convenience of performing a complicated task like OCR on an iPhone that I can slip in my pocket and that is always with me.
A few more points...
When I am using PDFpen Scan+ to scan a document, I use it on my iPhone, but the app also works on an iPad. It is far easier to take a picture using the easy to hold iPhone, and unless you have an old iPhone and a new iPad you probably have a better camera on your iPhone, so I recommend using this app as a scanner with your iPhone, not your iPad. But if you are working with a document scanned by another app or sent to you as a PDF file and you just want to use this app to do OCR, then PDFpen Scan+ is useful on the iPad.
Also, if you want to see PDFpen Scan+ in action, California attorney David Sparks prepared a video that you can see here on his MacSparky website.
PDFpen Scan+ is a decent scanner, but I cannot recommend it over Readdle's Scanner Pro. But the + in the name of this app refers to the OCR capabilities, and Smile Software gets an A+ for that + feature. If you are looking for a way to take a non-readable PDF file and turn it into a readable PDF file, PDFpen Scan+ is an excellent and useful app. Perhaps one day PDFpen Scan+ will get improved scanner capabilities, or perhaps one day Scanner Pro will gain the ability to OCR a document, and then we will have one app that does everything well. For now, if you do what I do and use PDFpen Scan+ in conjunction with Scanner Pro, you have a powerful combination.