How to restore only functions in windows I have taken function backup using following command: 

pg_dump -h localhost -u username -fc  -f db_dump dbname 


How to list the backup functions and how can I restore those functions to other database in windows?

Version is PostgreSQL 9.6.8
A dump generated with the -Fc option of pg_dump is in the custom format, which implies that it has a Table of Contents, which can be used to extract contents selectively.

As explained in pg_restore manual, the option to output the TOC is -l:

pg_restore -l db.dump &gt; db.list


This produces a file with one line per object, including functions, that can be edited manually to keep only the objects you're interested in.

Then a restore into another database could be done with:

  pg_restore -L db.list db.dump | psql -d otherdatabase [otheroptions]


If you were interested in extracting only a couple of functions, a quicker way could be to use the -P option to pg_restore:


  -P function-name(argtype [, ...]), --function=function-name(argtype [, ...])  
  
  Restore the named function only. Be careful to spell the function name and arguments
      exactly as they appear in the dump file's table of contents.