Is it possible to import/(copy in) a pdf-file including formulas and math to Lyx while keeping the math unchanged/editable/usable?
While with plain text there are rather few ways of expressing it, mathemathics writing is much more varied (in many cases more two dimensional than linear). Some crude approximation of text can be extracted from a PDF, but even if something like that could be made for your typical formula with subscripts, fractions and strange symbols, it will at best be very crude and require a lot of hand editing. Probably more work than just retyping the whole. If the PDF really is an image (not commands to place characters on the page, what PDF is really about) it is even more hopeless.