@magicalclick: NVM, turns out there's a variety of reasons why you might not be able to open a document on a WP:
You might not be able to edit a Microsoft Office document on your phone depending on what's in it or how it was last saved. Here are some of the more common things that make a document read-only on your phone.
The file is:
- Saved as an older type of Microsoft Office document, such as a Microsoft Word 97-2003 document (.doc), Microsoft Excel 97-2003 workbook (.xls), or Microsoft PowerPoint 97-2003 presentation (.ppt).
- Digitally signed.
- Marked as final.
- Protected using rights management.
- Protected with a password.
- Protected with restricted editing rights.
Microsoft Word documents are read-only if they have:
- Track Changes enabled.
- Custom markup (custom XML, Structured Document Tags (SDT), or smart tags).
- XML tags with unsupported values.
Microsoft Excel workbooks are read-only if they have:
- Functions that aren't supported on the phone. For info about which Excel functions are supported, see the Microsoft Support article about supported content in Excel Mobile.
- Data validation in one or more cells.
- Array formulas.
- Data tables.
- Macros enabled.
- Large column or row widths.
- Formulas that contain links or references to other workbooks.
- Formulas with structured references.
- Formulas that contain references, content, or formatting beyond cell IV16384.
- Formulas that are longer than 512 characters or have more than 30 arguments in them.
- Tracked changes.
- Dialog sheets.
- XML markup that isn't formed correctly.
- OLE objects or ActiveX controls.
For Microsoft OneNote notebooks, you can't edit:
- A page from a notebook that was sent as an email attachment.
- A notebook that is shared on SkyDrive, a Microsoft SharePoint site, or a SharePoint Online site, and marked as read-only.
- A notebook that has a corrupted page.
For Microsoft PowerPoint presentations, you can only make certain types of edits on your phone. Some examples include editing text in a text box, adding or editing notes, changing the order of slides, or hiding slides. For more info about editing a PowerPoint presentation on your phone, see Use PowerPoint Mobile.