Open the PDF and try to highlight a sentence. If you can't, the document has no text layer — Chat is reading it via OCR on the fly, and citation precision drops.
Run the OCR tool first to bake a text layer into the PDF, then upload the OCR'd version to Chat. Citations will be precise to the line.
If the PDF does have a text layer but citations still feel off, the issue is usually multi-column layouts. Mention the column in your prompt ("in the right-hand column on page 4…") and Chat will respect the boundary.