file not found. It's simple and yet it conveys all of the necessary information. To answer your question, the shortened messages would not be appropriate anywhere that formal language is used. ... "The file was not found" is grammatically proper.

Does not found or find?

As you wrote, only "I did not find" is correct. "I did not found" is an error. (There is also a verb "to found," but its meaning is different and it is not related to "find." "Find," with its past tense "found," comes from Old High German. "Found," as a separate verb, comes from Latin.)

Was not found meaning?

Not found is a negation of found. A single-word synonym for this phrase is unfound. Here's a list of synonyms for unfound. Adjective. Not previously encountered or found before.