> don't use JPEGs for schematics - GIF or PNG
PLEASE don't use JPG for clean line-art. Your CircusMaker surely emits very clean lines; JPEG with any compression past "1" will fuzz it up. Even good scans on yellowed paper, if you bump the contrast, will be much clearer in GIF or PNG than in JPG. Save JPG for nudes and landscapes, what it was made to do very well.
> old-fashioned MS Paint will open a .WMF file
Works in XP sp2. You may hafta right-click, "Open With..." to get it into Paint.
Paint, from at least XP days, does have Save As... GIF. It is also possible to do some annotation, crop, re-size, but very crude/limited.
IrfanView is free and very handy to have.
> get a pdf output file
PDF is great if it is a multi-page document. Also the usual PDF Readers will re-size to the user's convenience.
Another Win-trick. Get the PDF open big, hit Ctrl-PrntScrn. That puts your entire screen in the clipboard.
Alternatively, some PDF Readers have a mode to "Select Graphic". It has sometimes worked for me. This captures the selected area, instead of entire screen, to clipboard.
Now open Paint and "Paste Special". This pastes the clipboard as a new image. You can Save As...
Cropping in Paint is under-implemented. You can Select an area, Copy, close the original, then Paste Special and get the part you selected as a new image.
I strongly suggest finding PaintShop Pro version 3 to 7 in used-software sources. This will screen-capture, bump contrast, mark-up, re-size, and save to the usual formats. I tried a later version and felt shark-jumped... a few kewl features but nothing urgent, and the whole thing was very slow. V.5 was, IMHO, the high-point of the line as far as basic tech-image chores go (v.7 is better for photo flattery). The shareware versions are archived here http://www.oldapps.com/Paint_Shop_Pro.php but I do not recall what the trial-version limits were.