On tax day, April 17, I had a document problem.

My federal taxes were completed (I used TurboTax on my Mac), but I needed to fill out some paperwork to make a contribution to my retirement account.

This being the modern age, when I can file my taxes from my Mac without even looking at a mailbox, I forgot that transferring money from one account to pay for the IRA contribution would require a signature. In fact, it required the signatures of both my wife and me because the money came out of a joint account.

And here was the problem: I was at home, my wife was at work (with our car), and the paperwork needed to be signed and filed as soon as possible, because, of course, I had left this crucial step to the last minute.

Did I dash downtown on the next bus so my wife could sign the papers? Nope. I turned to our iPads and Smile Software's PDFpen for iPad (smilesoftware.com/PDFpen/iOS/).

I've used PDFpen on the Mac for years, typically when I need to make last-minute, save-my-bacon changes to PDFs, or often just when I need to paste an image of my signature onto a form. (The company also sells PDFpen Pro, with more features; I'm referring to both when I mention PDFpen for Mac here.)

(Apple's Preview application doesn't support that feature, nor does Adobe Acrobat Pro, which astounds me. I think I've run into PDFs that require an electronic signature less than a handful of times over the years — and that includes signing nondisclosure forms from Adobe itself!)

In this case, that's exactly what I did. Our financial adviser sent scans of the forms to me via email, and I used PDFpen to add my signature.

My wife, however, uses a Windows PC at work. We contemplated sending the PDFs to her email account, having her print them out and fax them to our adviser. But that would require her finding a working fax machine, and, besides, I really despise faxing in general; it's a technology that should have died out with parallel ports.

Then I remembered that she had her iPad in her bag. We could do the whole transaction electronically, and I wouldn't need to hop on a bus.

I bought PDFpen for iPad for $9.99 — currently an introductory price until May 1 — which is less than what I would have paid to have the forms faxed at a local FedEx office.

Over the phone, I shared my App Store information with my wife so that she could sign in as me and download the app to her iPad. Next, I sent the documents via email to her personal address, where they appeared in the Mail app. The iPad can read PDF files without a dedicated app, but since we wanted to open them in PDFpen for iPad, she touched-and-held the icon for the attachment, which brought up the option to "Open In" a compatible app. She chose PDFpen.

The next part was easy: She brought up the app's Markup tools, selected the free-form line tool, and signed her name on the appropriate line with her finger. After closing the document, she emailed the signed version directly to our adviser and to me, saving us all easily a couple of hours of trouble.

As you might guess, PDFpen for iPad is great for other PDF uses, too. The Markup tools let you highlight, cross out or underline text. It even includes a library of conventional proofing symbols you can add, as if you'd been working on a printed page with a pen. (And, yes, you can even make the ink appear red; copy editors rejoice!) You can also add photos stored on the iPad.

And with the app's latest release, you can opt to store documents using iCloud, making them available to the iPad and the Mac simultaneously. It requires PDFpen 5.7 or later.

If you bought PDFpen direct from Smile Software, you also need to purchase a 99-cent PDFpen Cloud Access app from the Mac App Store. (Only apps sold through the Mac App Store can tie into iCloud, one of Apple's restrictions; this tiny inexpensive app is a clever solution.) If you purchased PDFpen from the Mac App Store, you're set.

All of that is cool, no doubt, but I'm still most pleased with how PDFpen for iPad saved my tax day. If only it had helped me lower my tax bill.

Jeff Carlson and Glenn Fleishman write the Practical Mac column for Personal Technology and about technology in general for The Seattle Times and other publications. Send questions to carlsoncolumn@mac.com. More Practical Mac columns at www.seattletimes.com/ columnists.