Kindle Fire HD comes preloaded with OfficeSuite app. You can view word documents, spreadsheets, power point presentations with the Office Suite app. You can’t edit doc or docx files with it. Office Suite Pro has edit capabilities but costs about $15.
How to edit or view doc/xls/ppt files for free on Kindle Fire HD/2
1. Download & Install Kingsoft Office app on your Kindle Fire HD from Amazon AppStore.
2. You can edit doc/docx, xlx/xlsx, ppt/pptx files with it. You can search for the documents on your Kindle Fire HD.
KingSoft Office has integration with DropBox, Google Drive (Google Docs), Box.NET. You can upload edited and saved files to these cloud services. You can also use FTP your documents. You can email the edited documents directly from the KingSoft Office app.
I could not find any other free app for editing documents or excel files on Amazon AppStore. There are couple of android apps like OfficeSuite Professional 6, Documents To Go Full Version Key, but they cost about $15 bucks.
Also read, how to import iTunes playlists into Kindle Fire HD/2