You should save your CV as a PDF file, which retains formatting, doesn’t have spellcheck markup, is easy to open, and can’t be tampered with.
But if the job advert requests a different file format (e.g., .docx or Google Docs), always follow the employer’s instructions when you make a CV. Some companies use applicant tracking systems (ATS) that don’t read certain file types. If you ignore the employer’s instructions, they may never receive your carefully written CV.
The file name of your CV should be professional and easy-to-read. For example: Your-Name-CV-for-Company-Name.