NEW YORK — Even as a pared-down version of Microsoft's Office software package arrived on the iPhone, the company is holding out on extending that to the iPad and Android devices as it tries to boost sales of tablet computers running its own Windows system.
Microsoft also isn't selling Office Mobile for iPhone separately. Instead, it comes as part of a $100-a-year Office 365 subscription, which also lets you use Office on up to five Mac and Windows computers. Microsoft made the app available through Apple's app store Friday.
Microsoft Corp. is treading a fine line as it tries to make its subscription more compelling, without removing an advantage that tablet computers running Microsoft's Windows system now have — the ability to run popular Office programs such as Word, Excel and PowerPoint.
Microsoft has been pushing subscriptions as a way to get customers to keep paying for a product that has historically been sold in a single purchase. The company touts such benefits as the ability to run the package on multiple computers and get updates for free on a regular basis.
A subscription can be more expensive than buying the package outright for just one or two computers, but those wanting the iPhone app won't be able to avoid the recurring fees. Microsoft said it wants to give customers yet another reason to embrace subscriptions by offering Office on the iPhone only with a subscription.
The iPhone app will let people read and edit their text documents, spreadsheets and slide presentations at the doctor's office or at a soccer game. But many people will prefer doing those tasks on a tablet's larger screen. Office is available on those devices through a Web browser, but that requires a constant Internet connection, something many tablets don't have.
"The nature of the Office suite, being productivity-focused, makes it better-suited for a larger mobile screen," said Josh Olson, an analyst with Edward Jones. "The issue then becomes, 'How do you provide the Office offering in its best-suited mobile environment without negating a distinguishing characteristic of the Windows 8 tablets?'"
He said Microsoft isn't likely to offer Office on the iPad and other tablets until it sees sufficient adoption of Windows tablets first. Because of that, the new mobile app is likely to increase consumer awareness, but it won't significantly increase subscriptions.
Another analyst, Rick Sherlund of Nomura Securities, warned that delaying a tablet version on non-Windows devices will merely help competitors.
"Office is a bigger business for Microsoft than Windows, so we see more urgency to preserve and extend the Office franchise cross platform," he said.
Apple, for one, is refreshing its iWork package this fall, while Google bought Quickoffice last year. The two offerings are among several that are capable of working with Office files on mobile devices, though people using them may lose formatting and other details.
Chris Schneider, a marketing manager with Microsoft's Office team, would not comment on any plans for the iPad or Android.
The regular version of Office works on Windows 8 tablets, and most of the features are available on a version designed for tablets running a lightweight version of Windows called RT. Customers needing to use Office on a larger screen than a phone might be drawn to the Windows tablets, which have lagged behind in sales and cachet compared with Apple's iPad and various devices running Google's Android system.
The iPhone app comes with Word, Excel and PowerPoint and will sync with Microsoft's SkyDrive online storage service. Microsoft said people will be able to pick up a Word document exactly where they left off on another computer tied to the same account, while comments they add to a Word or Excel file will appear when they open it up on another machine.
Although documents will be reformatted to fit the phone's screen, the company said the iPhone app will preserve charts, animation, comments and other key properties. That's not always the case with programs offered by Google and other companies to work with Office files on mobile devices.
But the app doesn't offer the same range of features available on regular computers.
It's meant for lightweight editing, not complex calculations or heavy graphical work, Schneider said. Someone about to give a speech can review a PowerPoint presentation and fix a typo, for instance. Someone getting a Word or Excel document as an email attachment can add comments or make changes, then send it back, either as an email attachment or through a sharing feature on SkyDrive.
Rather than have it do everything, Schneider said, "we designed the Office Mobile for iPhone to meet the scenarios that make the most sense."
The iPhone app also won't have Outlook for email, Publisher for desktop publishing and Access for databases. Microsoft's OneNote software for note-taking has been available for free separately for iPhones and iPads.
People with Office 365 subscriptions will be able to run the new app on up to five iPhones, in addition to the five Mac or Windows computers. People in the United States were able to get it from Apple's app store Friday. Availability in other countries will follow in the coming days. Downloading is free, but a subscription is needed for the app to work.
It's possible to use the iPhone app on an iPad, but the documents are merely blown up to fit the size of the screen. You won't get to see more of a document despite the larger screen, and text and graphics won't look as sharp when enlarged.
Microsoft, which is based in Redmond, Wash., already makes a version for phones running its Windows Phone 8 operating system. An Office 365 subscription isn't required for that, and those apps do not count toward the five mobile devices permitted for each subscription.