How do I check if the fonts embedded in my PDF?

Your best consistent bet is to open the PDF file in Adobe Reader -- then File > Properties... > Fonts will list all fonts in the document. When you install Reader, it will install two browser plug-ins in /Library/Internet Plug-Ins that override the Safari PDF plug-in viewer.

I wrote a script that only reveals unique font names if the file was created by an OS X Quartz PDFContext (Print to PDF), or exported by Pages ’09 (v4.3). If your Word file is converted to PDF in a similar manner, the script may be of use. If the PDF is created by Acrobat Pro or other tools, the script usually doesn't work due to the PDF encoding issue.

Here is the Bash shell script for use in the Terminal. Crude.

#!/bin/bash
#
# print font names found in PDF written by OS X Quartz PDFContext 
usage () {
    printf "Usage:\n"
    printf "pdf-fonts.sh filename-1.pdf filename-2.pdf\n"
    printf "pdf-fonts.sh *.pdf\n"
    exit 1
}
for f in "$@"
do
#output sorted uniq font names
unset GREP_OPTIONS
printf "\n=== %s ===\n" "$f"
egrep -a -o '\+\b(.*\s)\b' "$f" | cut -d '/' -f1 | sort -u 
[[ $? > 0 ]] && usage
done
exit 0

and the output:

=== imgbullet.pdf ===

+Baskerville

+HelveticaNeue

+HelveticaNeue-Bold

+HelveticaNeue-Medium

+TimesNewRomanPSMT

Does embedded subset mean that those fonts are in fact embedded?

Yes.