What WMF is
Windows Metafile (WMF) is a graphics format from the 1990s that older Windows programs, early word processors, and some legacy publishing tools use for clip art and diagrams. A WMF file can hold drawing commands (a vector format) or a bitmap. PDF to WMF exists for the case where an old program will only accept a WMF file.
What this tool actually produces
PDF Studio renders each page to a small bitmap and wraps it in a WMF file with the standard placeable header. It does not convert the PDF’s text and shapes into editable vector drawing commands. A WMF drawing record can hold only a limited amount of data, so to stay within that limit each page is rendered at a deliberately small size — on the order of a hundred or so pixels across for a typical page.
The result is therefore a low-resolution picture of the page. It will open in programs that require WMF, but it will look blurry when enlarged and its text cannot be selected or edited.
When to use something else
If you need sharp images, use PDF to JPG or PDF to WebP, which render pages at twice their normal size. If you need scalable vector graphics, the best route is to open the PDF in a vector editor such as Inkscape or Illustrator and export from there. Use PDF to WMF only when a program specifically demands a .wmf file and a small preview-quality image is enough.
Practical details
You get one .wmf file per page, with a Download All button. WMF files open on Windows in programs such as older Office applications, and some cross-platform tools such as LibreOffice and Inkscape can read them. The conversion runs in your browser, so the PDF is not uploaded.