You could use versions of
psfrag that work with pdftex, but if you want to keep the latex/dvips/ps2pdf workflow you can convert the PDF to a sequence of eps files, for example the standard latex example document
sample2e.pdf is 3 pages, a command sequence such as
pdftops -eps -f 1 -l 1 sample2e.pdf sample2e-1.eps
pdftops -eps -f 2 -l 2 sample2e.pdf sample2e-2.eps
pdftops -eps -f 3 -l 3 sample2e.pdf sample2e-3.eps
pdftops is part of the widely available poppler tools
produces three EPS files sample2e-1.eps, sample2e-3.eps, sample2e-3.eps one for each page of the document, that you can then include into latex using graphicx in the usual way.