Skip to navigation
Real World Computing
Word 2013

Making sense of Office 2013's file formats

Posted on 20 Nov 2012 at 09:54

Simon Jones reveals some subtle changes to the file formats used in the latest version of Microsoft Office

Think back to the period 2006-9 and you might remember a great hoo-hah about Office file formats that rumbled on for years. Microsoft introduced its Office Open XML (OOXML) file formats – docx, xlsx and pptx – with Office 2007 and then sought to have them ratified as standards, first by Ecma (formerly known as the European Computer Manufacturers Association) and then by the ISO (the International Standards Organisation).

Many people asked why Microsoft hadn’t just used the existing Open Document Format (ODF) instead of inventing its own. Well, there wasn’t much wrong with ODF – except that it couldn’t represent everything in Microsoft Office documents, and back then it didn’t even define the functions you could use in a spreadsheet. Both ODF and OOXML are based on zipped XML text, making OOXML in particular far smaller and more robust than the old binary formats of DOC, XLS and PPT.

The Office Open XML file formats became an ISO standard in two flavours, Transitional and Strict

Steering OOXML through Ecma wasn’t too much of a problem for Microsoft, but ISO standardisation was far more difficult. ISO insisted that all the "legacy" features in OOXML – such as the options that said "lay out the document like Word 95", without defining what that was – should be corralled together with the intention of phasing them out.

Thus the Office Open XML file formats became an ISO standard in two flavours, Transitional and Strict – and neither Office 2007 nor 2010 could save in the Strict format since their internals still relied on some of those legacy features. Office 2010 could, however, open Strict Open XML files created by other applications, not that there were any mainstream applications that could write them. But the standard was published so that anyone could write an application that would create files in that format.

Now, with the impending release of Office 2013, you’ll be able to use Office to open and save Strict Open XML files as defined in ISO standard 29600. Their file extensions will remain the same – DOCX, XLSX, PPTX and so on – and the Strict format will not be the default format out of the box.

It will still offer a choice between Transitional Open XML and Open Document Format, but the ODF flavour will now be ODF 1.2. Providing ODF 1.2 gives better compatibility between Microsoft Office and OpenOffice or LibreOffice but, perversely, worse compatibility between Office 2013 and 2010 or 2007 when using ODF files.

Office 2007 and 2010 can save to only ODF 1.1 and can’t open ODF 1.2, but Office 2013 can’t save to ODF 1.1. This makes editing an ODF document in Office 2013 a one-way trip, since once it’s saved in ODF 1.2 format, you can’t then use it in Office 2007 or 2010.

Microsoft supported ODF 1.2 and its standardisation through OASIS, particularly in its definition of the functions used in its spreadsheets. Until ODF 1.2, they were left to individual companies writing the applications that used the ODF 1 and 1.1 formats, meaning that spreadsheets that were nominally saved in the same file format were in effect incompatible, because competing applications could read their data but none of their formulae.

ODF 1 is an ISO standard, but virtually no applications use it. ODF 1.2 is expected to be put forward for ISO ratification shortly; meanwhile, work on ODF continues, including adding change tracking to its specification.

Subscribe to PC Pro magazine. We'll give you 3 issues for £1 plus a free gift - click here
User comments

The defacto standard intechangable format is

I can use it on different versions of office and other programs.
All our office machines are set to save to this.
Saves hassle between us and customers, suppliers and staff with older machines.

By petermalins on 20 Nov 2012

Anyone actually use Open Office formats?

I've yet to meet anyone that uses OOXML

By JeffGranger on 20 Nov 2012


I've come across it a few times although it only seems to be businesses using it.

By tech3475 on 20 Nov 2012


The 97-2003 formats work with all versions of Office, Open Office, Libre Office, etc but they can't hold new features of MS Office such as Smart Art. They are also larger and more prone to corruption than OOXML formats.

OOXML formats are the default for MS Office 2007, 2010 and 2013 so are widely used but users of earlier versions (2000, XP & 2003) should install the Compatibility Pack so they can open and save the new formats too.

By Simon_Jones_RWC on 21 Nov 2012


If only...

Open Office and Libre Office make a complete pigs ear of importing / exporting documents - which can be very embarrassing.

At a previous employer, we had a customer turn up at a meeting with a PowerPoint presentation of their processes. The company only used OO.o and it opened the presentation without throwing up any errors, but all of the arrows from one process to another were randomly scattered over the slide, pointing to the wrong boxes!

By big_D on 26 Nov 2012


They only promise to open the files, not to show the data correctly, but they are getting better, particularly LO with OOXML files. (However, OO & LO presentation software is very weak compared to PowerPoint.)

I would not trust any conversion unless I could compare it side by side with the original. LO & OO are particularly bad at saying there may be some differences in layout but not saying what those are.

By Simon_Jones_RWC on 29 Nov 2012


Are you kidding me? Just to save in OOXML Strict instead of OOXML Traditional, I will have to upgrade to the ridiculously priced Office 2013 which doesn't even have upgrade versions? Where is my converter pack for older versions of Office to save in OOXML Strict?

By Anonymuos on 7 Dec 2012

Leave a comment

You need to Login or Register to comment.


Simon Jones

Simon Jones

Simon is a contributing editor to PC Pro. He's an independent IT consultant specialising in Microsoft Office, Visual Basic and SQL Server.

Read more More by Simon Jones


Latest Real World Computing
Latest Blog Posts Subscribe to our RSS Feeds
Latest News Stories Subscribe to our RSS Feeds
Latest ReviewsSubscribe to our RSS Feeds


Sponsored Links

Your email:

Your password:

remember me


Hitwise Top 10 Website 2010

PCPro-Computing in the Real World Printed from

Register to receive our regular email newsletter at

The newsletter contains links to our latest PC news, product reviews, features and how-to guides, plus special offers and competitions.