The default page format for OpenOffice is 
Letter. We could change it to A4 format by using the 
Page Style options.
- Click from the menu: Format > Page
- Under the Format Page section, choose the A4 format from the Format drop box.
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| Change the Page Style | 
Unfortunately, we have do these steps for each new document. To make this changes permanent, save this document as template, and set the saved template as the default one.
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| Save as template | 
- Create new OpenOffice document.
- Set the format, as discussed previously. template a
- Save as template: File > Template > Save. Give a name to the template.
- Set template as default: File > Template > Organize. Choose the template name that we had save previously. Click Commands on the right pane and choose Set As Default Template.
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| Set as default template | 
From now on, each new document will have format A4.