All of the "Office" document editing applications on the iPad have limitations. Best try them out to see if they meet your needs.
iWork by Apple
• VIEW/EDIT/CREATE Word & Excel files(Office 2007/2008/2010)
• VIEW PowerPoint, PDF, iWork, Text, .RTF, and more!
• Send & receive attached supported documents using the built-in Mail app
• FREE desktop application with your purchase! Compatible on Win & Mac allows you 2-way file sync with a WIFI connection.
• Open & Edit files within DocsToGo from any 3rd party app that supports the “Open In” feature
• Supports iTunes File Sharing via USB cable for manually moving files
"Office² HD, the most intuitive and straightforward office document editor available on the iPad, makes it easy to open, view, create and edit Word (DOC & DOCX), Excel (XLS & XLSX), and PowerPoint (PPT & PPTX) files right from your iPad!"
Quickoffice Pro HD
Create and edit ALL Microsoft® Office -- document, spreadsheet, and presentation formats, as well as view PDF files, on the go. Our advanced file manager lets you manage local files, access Google Drive or other cloud accounts, and works with your iPad email attachments so you can work anywhere, anytime - online and offline.
nsdjoey presents ways to edit office documents in this web page:
I use Office2HD on my iPad and love it. Its only $7.99 and works great to view and/or edit Word, Excel, and PowerPoint docs. I use the free Dropbox integration so that everything is saved in the cloud. I can start a document at my desk on my computer and work on it on my iPad when I'm out of the office…then go back to my desk later and see the changes. Not bad for $7.99.
Hope this helps!