When you double click a file in Mac OS X, Finder tells you that there is no default application specified to open the file. When this happens, Finder does not open the file unless you tell it which application can read the file. How do you determine whether you have an application that can read the file, and which is the best one for it? Well, there are several reasons Finder may not know how to read a file, and you may need to use trial and error to determine which reason is plaguing your particular file. The four most common problems are:
- You truly do not have any software that can read the file.
- You have software that can read the file, but the file is corrupt, and therefore, cannot be opened.
- You have software that can read the file, but the Finder cannot determine what kind of file it is, and therefore, does not associate any application with it.
- You have software that can read the file, but the software does not tell the Finder that it can read the file, so you must manually open the file from within the software.
Finder does not know what to do with this file, but if you select “Choose Application,” you can tell Finder which application should open the file.
While you certainly can open each application on your computer and then see if the application can read the file, it is likely to be faster if you try to determine what type of file you have. You can then determine if you have the appropriate software to open it, and if not, which software you will need.
One of the easiest ways to find an application to open your file is to search the App Store, at least if you are using the latest version of Snow Leopard or Lion. When developers submit applications to the App Store, they can specify types of files their applications can open, and they have two ways to do that: tell Apple which file extensions an application opens, or which UTIs (uniform type identifiers) to associate with an application.
Let’s say you wanted to open a PDF, but you didn’t have an application to do it. There are two ways you can ask the App Store to search for an application that opens your file. First, if you have tried opening the file but get the error message in the above image, you can press “Search App Store.” Second, you can click on the file in the Finder, go to the File menu, and select Open With –> App Store. Either way, the App Store application opens and begins searching.
Here’s the tricky part: if the Finder can identify a file’s UTI in the file’s metadata, the App Store searches by metadata. This is the preferred method. If it can’t determine the UTI, it searches by file extension, if there is one. The problem with searching by file extension is that some applications’ files share the same extensions, even though the files are very different. For example, most PDF files on a Mac are Adobe Acrobat files. They can be, however, Netware printer definition files, Ed-Scan graphic files, or several others. An Acrobat PDF’s UTI should always be com.adobe.pdf, so there’s little risk the App Store will show you applications that cannot open the file.
Finding Files’ UTI Metadata
If your file is in working order and Spotlight has scanned it, you may be able to find its UTI from the Terminal. Open Terminal and type: “mdls /path/to/yourfile” (without the quotes). Terminal will spit out quite a bit of information about your file. Scroll back up until you see the line marked “kMDItemContentType.” The file’s UTI is the value associated with this variable.
Searching the App Store by File Extension or UTI
If you want to quickly find applications in the App Store that can open a specific file extension or UTI, you can specify this in your search. To search by file extension, simply type, “extension:” (without the quotes) followed by the extension characters. For example, to search by the extension .PDF, type: extension:pdf. To search by UTI, type, “uti:” (without the quotes) followed by the UTI string. For example, to search for the UTI com.adobe.pdf, type: uti:com.adobe.pdf.
If you still cannot figure out what kind of file you have or which applications can open your file, there are several ways to investigate. It’s generally easier if your file has an extension, but even if it does not, this guide can point you in the right direction.
Caution! By completing the following troubleshooting steps, there is a small chance that your file will become unreadable by its proper application. This is because some applications change data in the file without asking you, and if the wrong application is the one changing the data, your file may become corrupt. Therefore, you should duplicate the file in question and work off of the copied file. That way, you still have the original, untouched file if things go awry. (You can duplicate a file by selecting it in the Finder and choosing Duplicate from the Finder’s File menu.)
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