Microsoft Office/Things to Know When Saving

There are a menagerie of ways you can save a file in Microsoft Office, each with their own features and limitations. However, on a default windows installation, you might not be able to necessarily see the difference. This necessitates the enabling of file extensions, which represent the different types of file formats a Word, Excel, or PowerPoint document can be saved as. Think of these as a form of language your computer's word processor reads to spit out English back to you.

What's a file extension?

Every computer has a menagerie of programs, like Word, PowerPoint, and Excel, that read documents, which are also known as files. To prevent accidental re-writing of files intended for different programs, file extensions are used to distinguish between files that can be read, and files that should be avoided whenever a program needs to read a file.

A quick summary

Text

.doc - The old Microsoft Word file format.
.docx - The new Microsoft Word file format. Saves by default.
.docm - The new Microsoft Word file format with macros enabled. Dangerous.
.odt - The OpenDocument format, used by OpenOffice, and its successor, LibreOffice.

Slideshows

.ppt - The old Microsoft PowerPoint file format.
.pptx - The new Microsoft PowerPoint file format. Saves by default.
.pptm - The new Microsoft PowerPoint file format with macros enabled. Dangerous.
.pps - The old Microsoft PowerPoint file format with automatic slideshows.
.ppsx - The new Microsoft PowerPoint file format with automatic slideshows.

Spreadsheets

.xls - The old Microsoft Excel file format.
.xlsx - The new Microsoft Excel file format. Saves by default.
.xlsm - The new Microsoft Excel file format with macros enabled. Dangerous.
.xlsb - The Excel binary format. More information to come...

Macros

In the past, it used to be a roll of the die whether a document received had viruses or not. Starting with Office 2000, Microsoft restricted running macros by default, but they were still easily enabled. With the release of Office 2007, Microsoft further locked down macro access; the new .docx, .pptx, and .xlsx files do not support macros. Instead, the corresponding macro-enabled OOXML-transitional Office document files now end in .docm, .pptm, and .xlsm.

But wait: What's OOXML? For that, we have to walk through the history of the standardization of word processor documents.

A brief history

For the sake of simplicity, we won't be covering obsolete, or uncommon file formats like those from WordPerfect or Lotus. However, Microsoft Word and Excel should be able to read and convert most of these files. No promises that there won't be errors though; these old, proprietary formats are not standardized whatsoever.

XML extensions for Office 2003

Prior to Office 2003, the only way to save a document with readable markup would have been to save the document as an HTML file. However, since HTML was mainly designed for the web, this was a huge annoyance to book writers, who wanted an easy way to change their book's markup, via Microsoft Word, without having to write the whole book in raw XML markup.

Enter Office 2003. Microsoft introduced the readable, albeit proprietary, WordML and SpreadsheetML to the .doc and .xls file formats of the day. This replaced the unreadable, proprietary .doc and .xls file format from Office 2000 and prior.

OASIS OpenDocument

Sun Microsystems had purchased a relatively obscure alternative Office suite called StarOffice. However, in an effort to stay competitive with Microsoft Office, Sun Microsystems opened up the StarOffice formats for use by everyone. Hence the rise of .odt and the standardization of OpenDoucment as an ISO format.

Currently, the most up-to-date Office suite using OpenDocument as its primary file format is LibreOffice.

OOXML Office 2007 "transitional"

Back to Office 2003. So Microsoft had this XML format that they shoehorned in to the .doc and .xls format. Now that OpenDocument was competing with Microsoft to become the world's standard document format, Microsoft responded with "Office Open XML", also known as "OOXML".

However, since Microsoft had just introduced XML support to Office 2003, they had to find some way to allow WordML and SpreadsheetML users to use the new OOXML format. Instead of leaving out Office 2003 users, Microsoft integrated WordML and SpreadsheetML in Office 2007's new Word and Excel file formats (.docx, .xlsx), along with parts of OOXML, creating a new file format, technically incompatible with the official ISO spec. This spec is called OOXML "Transitional" (ISO/IEC 29500 Transitional).

However, due to the fact that Microsoft was unable to release a version of Office compatible with the official ISO spec, to the disapproval of governments involved in the ISO, Microsoft added OpenDocument support with the release of Service Pack 2 for Office 2007.

OOXML Office 2013 "strict"

Office 2013 was the first version of Office to support the official ISO OOXML specification, here called "OOXML-strict". However, due to the proliferation of "OOXML-transitional" documents, as well as the need to maintain comparability with Office 2007 and Office 2010, it isn't chosen as the default file format whenever an Office document is saved.

Too complicated?

Just follow this checklist for what to ask before sending a document. If something doesn't apply to you, cross it out. Stop when a point applies to you.

If your recipients use OpenOffice: Use OpenDocument. (.odt). OpenOffice does not support Office Open very well at all. If you can't afford Microsoft Office, consider moving to LibreOffice.
If your recipients use LibreOffice: Use OpenDocument (.odt) or Office Open (.docx). Both will work, but OpenDocument is definitely preferred.
If your recipients use an old version of Office (from 2003 and prior): You must use classic Office (.doc)
If your recipients use a Mac with Office 2013 (or later) installed: Use Office Open "Strict". You may have to hunt for this in the drop-down menu, as it has the same format (.docx). However, choosing "strict" may prevent minor formatting errors when communicating between PCs and Macs.
If your recipients use a Mac: Use Office Open (.docx). You may experience some formatting errors, so beware.
If your recipients use Office 2007-2010: You cannot use Office Open "Strict". Cross out all other "strict" points left in this checklist. Then continue.