Proquest book can download in Adobe digital editions, it is a free pc software from adobe, just open this site and then download and install the software: https://www.adobe.com/solutions/ebook/digital-editions/download.html,
ePub converter can convert proquest book to pdf sometime ago, but Proquest.com update them server to new DRM protection that can’t decrypt by now, you got error message like this
epub converter and other converter doesn’t work with new ADEPT, but we provide 2 way to convert proquest book to pdf,
ProQuest Downloader
Proquest book can view in browser, we have chance to convert browser cache to pdf book, PorQuest Downloader is this tools,

you need to be signed in to proquest website, then open the page of the book you want to download in app, click “Download” button when it ready, app will download book automatically.
Adobe Digital Edition Converter
