Exporting to a PDF can be a bit tricky when using Power BI Desktop. The following may make your task a bit easier:
- The resolution of exported report pages is 1280 pixels x 720 pixels ref: https://docs.microsoft.com/en-us/power-bi/consumer/end-user-pdf?tabs=powerbi-desktop
- Most important: Ensure all pages are using the Page view mode of “Fit to page” before you attempt an export.