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FolderSizes Help

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File Extensions

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The FolderSizes File Extension Researcher tool helps you to determine the potential function (or application association) of a given file extension (such as ".PDF" or ".DOC").


It's important to understand that there is no central authority governing the use of file extensions by software applications. So even though many file extensions are predominantly associated with a single application (e.g. ".doc" = Microsoft Word Document), such direct associations are absolutely not guaranteed. Further, you will often encounter file extensions for which the operating system has no known software association. The File Extension Researcher helps you to determine the potential origin of such files.


To use the File Extension Researcher, enter a file extension (such as ".pdf" or ".doc") and click the Go button. You will be presented with two distinct pieces of information:


Shell Association - The operating system shell has special, intrinsic knowledge of some file types and their application associations. The shell uses this knowledge to (among other things) open files with specific extensions with a default application.

All Potential Associations - This is a more complete listing of functional / application associations. This list will often yield results even when the Windows shell has no knowledge of a particular file extension.


The "All Potential Associations" listing shown within the File Extension Researcher pulls information from a file extension database contained within FolderSizes. This database contains thousands of mappings between file extensions and application / functional associations, but it can never be entirely complete (because there's no central registry for file extensions from which to cull such data).


You can also click the Research Online button, which will launch your web browser and search for details (and other potential associations) on the file extension you entered. Note that the source for such information will generally be a third-party website that specializes in it (and has no association with FolderSizes or its parent company, Key Metric Software).


Finally, you can browse the entire file extension database contained within FolderSizes by clicking the "View All Extensions" button. The resulting window will allow you to browse known file extensions by their first letter, or by numeric / symbolic grouping.