Vim has a few modes for autocomplete. All of them start with <kbd>Ctrl x</kbd>. You can trigger autocomplete for whole lines, words from dictionary, or even word suggestions from thesaurus.
If you need to get a path from any buffer, try <kbd>Ctrl x</kbd><kbd>Ctrl f</kbd>. This way you can browse through the whole tree starting from current directory if
$PATH is set correctly.