Why can't I get any model to read/analyze PDFs in LM Studio??

I've tried Mistral 3 3B, Qwen 3.5 2B, and Gemma 4 e2B. Attach a 56 page 1.8MB machine readable PDF. LM Studio gives me a popup introducing its RAG feature saying "You can now chat with your own documents using Retrieval Augmented Generation (RAG)." I ask very specific questions to the model, asking it to summarize the attached PDF. I see the Assistant notifying me that it's Loading and Processing the PDF. I keep getting either "I can't access it" or "No file was attached". What am I doing wrong