Hi hayem,
there are several Office suites which will do the job. Some have a price tag and some are free, as far as I can remember, but a quick AppStore search will show.
QuickOffice Pro HD
DocsToGo
Smart Office 2
Office2 HD
Polaris Office
And then there are individual Apps like Keynote (for presentations) and numbers (for spreadsheets).
These last apps import PPT and XLS files. You can export revised versions of your files using MS Office or iWorks file formats or use PDF.
Hope this helps.
Knut