Another good option is PDF GPT, which is geared specifically for summarizing, answering questions, translating and providing citations for PDF documents. It can handle a variety of documents and can respond quickly in more than 90 languages. PDF GPT's Pro version costs $6 a month and lifts file upload and page limits.
ChatDOC is another option. You can upload various files, including PDFs, and get immediate answers to questions. The tool can handle deep AI analysis, multi-document conversations and even math formula analysis. It comes with a browser extension for uploading and citing answers, and is geared for students, professionals and businesses.
If you're looking to focus on academic papers, Scholarcy has a summarization tool geared specifically for the job. It turns dense documents into interactive summary flashcards and offers features like custom summaries and note-taking. It's designed to help you work more efficiently while doing research, and is good for students and researchers.