Windows MetaFile files are vector image graphics that appeared along with Windows XP. However, they suffer somewhat from security problems and obsolescence, meaning they are not well supported in later versions of Windows.
There are two ways of quickly managing these WMF files. One is to use a Windows XP-based computer, and the other is to use the Office Picture Manager included in Microsoft Office. Neither of these is particularly pleasing for users of lean, modern computers, especially since there is no thumbnail viewing in the file explorer. The easiest way is to convert these files to another format.
The best utility to convert these, based on price, simplicity and effectiveness, is the Bulk Image Converter, a free open source utility that requires no installation and has a very small size. Simply select the files, choose the final file format, and go.
Be aware that since WMF files are vector formats, conversion to a non-vector graphic format, such as JPG or PNG, will result in pixelation in some cases. Converting WMF files to high-quality, pixel-dense JPGs will retain much of this quality, but also take up a large amount of space. The Bulk Image Converter also does not have options for quality output.