Opera Help and Support

Downloads and File Types
Opera handles a large number of varying file types, including HTML files, graphical files such as JPEG and GIF, and other types of files which it cannot use by itself. These include PDF documents, word-processor documents which can end in SXW, RTF, DOC, or any of a dozen other extensions. For certain file types, Opera needs multimedia plug-ins.

Configuring settings
By default, Opera will determine how to handle a file by its MIME type. MIME types are descriptions used by Web servers to identify files to browsers. This is the most secure way of receiving content on the Internet. There is a second option, however; you may choose to let Opera determine use the file's extension to decide which action to take when the MIME type is not reliable. This option is less secure than the default.

Some MIME types are intended as generic types, such as "text/plain" and "application/octet-stream". If a server is not specifically set up to handle a certain kind of content, these generic MIME types are often used. This means that sometimes a video file in an MPEG format will be sent using the "text/plain"MIME type. If you have chosen to determine action by file extension, Opera will nevertheless recognize the video file's extension (such as ".mpg"), and handle it according to your settings for .mpg files.

However, sometimes the file type indicated by the extension is not the file type that the browser interprets. This is due to an HTTP header called "content-disposition," which can assign a new name to the file you are downloading. Therefore, if you enable the option to determine file type by extension, pay close attention to the file name in "Open" and "Save" dialog boxes and make certain the file is not of a different kind than expected. If it is, do not open or run the file.
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