Chrome: DriveConverter expands on Google Drive's built-in file conversion tools to allow users to convert uploaded files to a larger variety of formats.
The service doesn't work on Google Drive files themselves, but you can convert those to different formats when downloading, so this actually avoids redundant features. This extension works on your uploaded files instead, offering some incentive over Dropbox (which doesn't allow for in-app add-ons like these). Once you install the extension, reload Drive and right-click on the file you want to convert. DriveConverter supports the following formats:
From: docx, doc, txt, rtf To: pdf, xml, rtf, doc, docx, html, txt
From xlx, xlsx To: pdf, csv, txt, html, xlsx
From: png, jpg, gif, bitmap, tiff To: png, jpg, gif, bitmap, tiff
From: mp3, mp4, m4a, flac, wav, ogg To: mp3, mp4, m4a, flac, wav, ogg
For those concerned about security, DriveConverter only accesses files you allow and the company says that all files are deleted after they're converted.