In QuickBooks Online, we can only import Excel files with CSV or XLS/XLSX format. I suggest converting your PDF files first into an Excel file before you can bring them in QuickBooks Online. You can look for a third-party app that can convert the file or visit our QuickBooks Apps Store.
Additionally, we can import a QBO or QFX files if it's a bank transactions. You can get these files through your bank's website. I've added these articles for your reference: