The quick office app that came pre installed on my desire opened up a xlsx no problem
According to the Quick Office Site.
Their version for Android will only open .doc and .xls
Quickoffice Quickoffice for Android or see below:
View Word and Excel Office Files on Your G1.
Access
Access your Word (.doc) and Excel (.xls) files from memory card or from GMail attachments.
View
Simple to use features provide a rich user viewing experience only available with Quickoffice.
Word and Excel Common Features
Open .doc and .xls files from memory card or from Gmail attachments
Easily Zoom in or out
Smooth scrolling throughout the application.
Orientation automatically adjusted based on the sensor
Word Viewer Features
Text wrapped doc display eliminates left-right scrolls
Displays all formatting, bulleted and numbered lists, tables and images
Follows telephone numbers, hyperlinks, and email addresses
Fast first page view to quickly identify document
Excel Viewer Features
Spreadsheets display in familiar Excel UI
Resize column and row
Display cell content with cell and number formatting
Manage
Manage your files from memory card with our easy to use file manager.
Navigate folders
Rename, delete and view file properties
Sort file listings by file name, type, size and date modified
Files Formats Supported:
Microsoft Word: .doc
Microsoft Excel: .xls
Text Files: .txt
Please Note: Quickoffice for Android supports viewing for 2003 and earlier versions of Microsoft Word and Excel documents. Office 2007 documents for Word (.docx) and Excel (.xlsx) files are not supported in this release.
Quickoffice for Android does not support document EDIT at this time.
Stay tuned for more information on availability of Powerpoint viewing and Office editing.
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Language Support:
English
Requirements:
Google Android 1.0 Operating System