- set variable s to that string: -v s='=== /C=IN/OU=emSign PKI/O=eMudhra Technologies Limited/CN=emSign ECC Root CA - G3'
- on lines matching the regex between //, set skip to false: /^(===|###) /{skip=0}
- on lines matching s, set skip to true: $0==s{skip=1}
- if skip is false, print the line: !skip
Note the last part where it just says !skip without a curly braces. AWK defaults to print in that case.