If you wish to do any kind of modding for Synergy, you'll have to set up Source SDK first.
To do this, you must follow the instructions below:
"Synergy"
{
"GameDir" "C:\Program Files\Steam\SteamApps\ \synergy\synergy"
"hammer"
{
"GameData0" "C:\Program Files\Steam\SteamApps\ \synergy\synergy\SDK\synergy.fgd"
"BSP" "C:\Program Files\Steam\SteamApps\ \sourcesdk\bin\orangebox\bin\vbsp.exe"
"Vis" "C:\Program Files\Steam\SteamApps\ \sourcesdk\bin\orangebox\bin\vvis.exe"
"Light" "C:\Program Files\Steam\SteamApps\ \sourcesdk\bin\orangebox\bin\vrad.exe"
"MapDir" "C:\Program Files\Steam\SteamApps\ \sourcesdk_content\synergy\mapsrc"
"GameExe" "C:\Program Files\Steam\SteamApps\ \synergy\hl2.exe"
"GameExeDir" "C:\Program Files\Steam\SteamApps\ \synergy"
"BSPDir" "C:\Program Files\Steam\SteamApps\ \synergy\synergy\maps"
"TextureFormat" "5"
"MapFormat" "4"
"DefaultTextureScale" "0.250000"
"DefaultLightmapScale" "16"
"DefaultSolidEntity" "func_detail"
"DefaultPointEntity" "info_player_coop"
"CordonTexture" "tools\toolsskybox"
"MaterialExcludeCount" "0"
}
}