Adding "Responsible for official written communication" is too vague to be worthwhile in a resume. "official written communication" could be anything from legal documents to emails with customers. You need to be more specific about what exactly you were responsible for. Here are some examples of things that might be worth including in your resume:
- Responsible for creating official company press release statements [include link to example]
- Managed company's official social media account [include link]
- Provided regular project reports to customers
- Prepared legal contracts for company merger
Or whatever it is you actually did. Be specific, and be relevant to the job you are applying for. If you want to work in PR, then the fact that you ran the company's social media accounts is important. If you want to be on the company's legal team, then it may be less important. That's up for you to judge.