Do you have to run in a 10k or can you walk?
It's perfectly OK to walk in most 10k races (although more
people will be running than walking), especially if the race is
titled "10k run/walk." However, if it's specifically called a "10k
run," you might want to email the race organizers and ask if it's
OK to walk. Sometimes a race has a "5k run/walk" and a "10k run,"
meaning that you can run and/or walk in the 5k but can only run in
the 10k.
Basically, it's most likely that walking is totally fine. It's
not like they can disqualify you for walking, anyway.