Open the Select Correct Document Format dialog by Add ‣ Existing document item in the Project View context menu or by File ‣ Open As item in the main menu. The foolowing dialog will appear:

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     <img src="/wiki/download/attachments/4227228/Advanced Dialog Options.png"/>
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Here you can choose how to interpret the data stored in the file. The format is detected automatically, but you can select it manually.