Why Preview doesn't show always power terms (m^2 etc) in pdf?

Question

There is clear cap between letters but the number is missing.
Like this one
Between m an K should be a 2 but it has vanished for some reason. If I look same document with PC the power term is in it's right place.
But sometimes it works. Like in this one:
This is from same document but different page.
And if power term is missing from a formula the answer will be wrong.
I can not use this type of unreliable software. How can I fix this?
(The whole document is here http://www.ym.fi/download/noname/%7B8C5C3B41-E127-4889-95B0-285E9223DEE6%7D/4046 8 )
I'm using iMac SO X Yosemite 10.10.3.
Have anyone noticed same problem?

Answer 1

Thank  you for your reply.
Indeed, I tried saving a PDF that had the "default appearance", it shows exactly the same. So it looks like it "can't" show the image.
However, of course, I do want the image to be shown. How can I achieve this? How can I tell Adobe Reader (and other PDF viewers) I really really realllyyyyy want to see that image there? I believe I'm not doing anything really exotic, right? There must have been tons of other people that wanted to do the same thing, I guess?
                    var annotation = new PDFLinkAnnotation
                                Action = new PDFUriAction(this.GetCodeUrl(code)),
                                Contents = AnnotationIdentifier,
                                Appearance = new PDFImageAppearance(bitmapImage),
                                DisplayRectangle =
                                    new DisplayRectangle(
                                    barcodeLocationInfo.X,
                                    barcodeLocationInfo.Y,
                                    barcodeLocationInfo.Tsw,
                                    barcodeLocationInfo.Tsh),
                                Flags = Flags
                    pdfPage.Annotations.Add(annotation);