The used fonts can be displayed e.g. using pdffonts:
$ pdffonts schmidt.pdf
name type emb sub uni object ID
------------------------------------ ----------------- --- --- --- ---------
SKGHXE+URWPalladioL-Roma Type 1 yes yes no 32 0
RGGMAD+CMSS10 Type 1 yes yes no 36 0
SRMKXJ+CMTT12 Type 1 yes yes no 40 0
MEAKIS+URWPalladioL-Bold Type 1 yes yes no 43 0
XMXATW+URWPalladioL-Roma-Slant_167 Type 1 yes yes no 46 0
YMJOFK+URWPalladioL-Ital Type 1 yes yes no 49 0
YYGKBG+TeXPalladioL-SC Type 1 yes yes no 52 0
LTFGIL+URWPalladioL-BoldItal Type 1 yes yes no 62 0
FFQSQZ+CMR12 Type 1 yes yes no 66 0
WYBEJZ+CMSS12 Type 1 yes yes no 69 0
VNYREA+PazoMath-Italic Type 1 yes yes no 103 0
It looks to me it uses the mathpazo package/font.
pdffontscommand really helps! – FloydChen May 20 '11 at 17:30