With that said, it is possible to bold, italicize, underline, and change the color of text in the SRT file using our beta website, InqScribe Labs. Note that this will involve adding HTML-style markup into your transcript, uploading the .inqscr file to our site, and then downloading the resulting SubRip SRT file. If you already plan on moving the file into Premiere, it will most likely be easiest to style the text inside the Premiere editor. For more info about using in-line markup, head over to the SubRip exporter section of our InqScribe Labs website here.
Note: Unfortunately, it seems that Premiere is lacking the feature to increase subtitle resolution. In other words, there isn't an option for "HD" or "4K" subtitles. Our understanding is that imported subtitles cannot exceed 720x480 (source).
If you have questions or comments to add, feel free to contact us at firstname.lastname@example.org.