Here is the full list of all 54 Day of Defeat: Source achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Score 5 consecutive headshots in a single round without dying
Score 8 machinegun kills from a single deployed position
Win a knife fight
Play on 5 non-official Day of Defeat Source maps
Kill 4 or more players with a single grenade, riflegrenade or bazooka shot
Kill a deployed sniper or machinegunner from a distance greater than 100 feet with a rocket
In a single life, kill 4 or more players in the victory time after winning a round
Capture the final flag to win a round
Score 5 or more kills in a single life using scavenged enemy weapons
Win Dod_Colmar without the other team detonating any bombs on your objectives
Get 5000 kills as an Allied player
Get 5000 kills as an Axis player
Get 1000 kills as the Rifleman player class
Get 1000 kills as the Assault player class
Get 1000 kills as the Support player class
Get 1000 kills as the Sniper player class
Get 1000 kills as the Machinegunner player class
Get 1000 kills as the Rocket player class
Get 500 kills with the Garand
Get 500 kills with the Thompson
Get 500 kills with the BAR
Get 500 kills with the Springfield
Get 500 kills with the .30 Cal
Get 500 kills with the Bazooka
Get 500 kills with the K98k
Get 500 kills with the MP40
Get 500 kills with the MP44
Get 500 kills with the K98 Sniper Rifle
Get 500 kills with the MG42
Get 500 kills with the Pschreck
Get 150 kills with the Colt
Get 150 kills with the P38
Get 150 kills with the C96
Get 150 kills with the M1 Carbine
Get 150 kills with the Knife
Get 150 kills with the Shovel
Get 150 kills with your fists
Get 250 kills with the US Frag Grenade
Get 250 kills with the Stick Grenade
Get 250 kills with the Garand's Rifle Grenade
Get 250 kills with the K98k's Rifle Grenade
Score 100 Flag Captures
Win 100 rounds
Plant 100 bombs on enemy objectives
Defuse 100 enemy bombs
Complete All Achievements
Win a round on each of the winter themed maps: Dod_Kalt and Dod_Colmar
Collect three gifts dropped by opponents.
Kill an enemy by throwing back one of their team's grenades or riflegrenades
Kill a machinegunner who has killed 8 or more players from a single deployed position
Block a Flag Capture that would have won the round for the enemy team
In Dod_Jagd, plant a bomb that explodes in overtime to extend the round
In a single life, get a kill with an MG, Sniper Rifle, Rifle, SubMG and a Grenade
Block 100 Flag Captures