Lillian Lim noticed strange files appearing and disappearing. The file names always begin with ~$.
If you don't know what's going on, these files can be confusing--and even scary. A file appears in your Documents folder without you intentionally creating it. Aside from the strange punctuation, the file name looks familiar. The icon and, if visible, the extension tell you that you can open the file in a common application. But when you double-click the file, or try to delete it, you get an error message.
Then the file disappears as inexplicitly as it appears. Except for those occasions when it doesn't disappear at all.
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Don't worry. These are merely temporary files created by either Word or PowerPoint. They appear when you open a document or a presentation, and they usually disappear when you close it.
These temporary files have almost the same file name and extension as the files they're ghosting. Word replaces the first two letters of the file name with ~$, while PowerPoint adds those two characters to the beginning of the name without removing anything. For instance, when you open Attack of the Blood Beast.docx and Hercules Against the Moon Men.pptx, you'll get the temporary files ~$tack of the Blood Beast.docx and ~$Hercules Against the Moon Men.pptx.
You can't open these files because, despite their extensions, they're not normal .docx and .pptx files. And you can't delete them because they're in use. Or at least the PowerPoint files are in use. In my experience, you can delete the ~$.docx files.
You'll occasionally see a ~$ file when the real file isn't open. When Word or PowerPoint fail to close properly--for instance, in a Windows crash--the files aren't automatically deleted.
Actually, you're not supposed to see these files at all--they're hidden files. The fact that you can see them tells me that you (or someone else) has set up Windows to display hidden files. You can hide or reveal hidden files in the Folder Options dialog box, on the View tab.