PostgreSQL 9.4 database cannot be saved with pgAdmin 3 (Windows 8.1)

You need to tell pgAdmin to use the 9.4 binaries, through the "Binary paths" section in the options dialog:

https://www.pgadmin.org/docs/pgadmin3/1.22.2/options-browser.html

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your pgAdmin version is a bit old as well. 1.20 ships with Postgres 9.4, not 1.18

Also I found very effective to just replace pg_dump.exe in pgadmin version folder with my pg_dump.exe from my Postgres database.

I see why the solution above is better, but if someone would have problems with that, this also seems like functional alternative.