: Season 7 (Series 7) of the modern show only contains 13 episodes plus specials, so an "Episode 18" does not exist in standard modern numbering.
: Platforms like SubSource and TVsubtitles.net offer downloadable SRT files for entire seasons, including Season 7. Doctor Who subtitles English S07E18
: Classic "Doctor Who" episodes, complete with closed captioning, are available on BritBox and Tubi. Note on Numbering : Season 7 (Series 7) of the modern
If you are looking for English subtitles for this specific episode, you can find them through several dedicated resources: Subtitle Resources complete with closed captioning