I would like to find out how to write an official company introductory letter.

This website will show you all you need to know

WriteExpress: Letters and Templates for Microsoft Office

Not sure I know what you mean by "official company letter"? If you are sending a resume to a company where you seek employment, the following might be helpful. If you want a letter to introduce your company to a potential client, disregard the following.

Use the KISS principle... keep it simple, stupid.

Most of the information about you will be in the resume that you attach. All you need in the introductory letter is the job you are applying for and maybe a couple of sentences pointing to information in your resume that says you are qualified for the job. No one is going to read any more than this. If you appear at all qualified, they will spend much more time on the resume.

Since you will probably be sending your resume out to a number of different companies, you'll have to tailor the letter to match the job offered by each of companies you send your resume to.

There are also links at the bottom of this page to questions that have been similar to yours. You might want to click on them and see what some of the answers have been.l