Yes, you should capitalize abbreviations when writing them in a formal document.
Yes, events should be capitalized when writing formal invitations.
In a formal writing, yes. In an informal writing, you don't have to.
You are writing a business letter, you should be more formal.
An extended formal document is writing to someone in a formal extended way.
Résumé
Most people use "incl." However, for formal writing, you should just spell it out. This is true of most abbreviations in formal language.
No, you would italicize the name "Netflix" when writing it in a formal document or publication.
An example of abbreviating the year with an apostrophe in a formal document would be writing "The event took place on June 15, '21."
In formal documents or academic writing, years can be abbreviated by using the last two digits of the year followed by an apostrophe. For example, 1998 can be abbreviated as '98.
When writing height in a formal document, use feet and inches. For example, write "5 feet 10 inches" instead of using symbols like ' or ". This format is clear and professional.
Capitalize family titles when they are used as names. For example, "Where are you going, Dad?" Do nott capitalize family titles when they come after a possessive noun or pronoun or an article. For example, My sister teaches at the university.
The introduction to a formal document is called a preamble.