All the methods common to macOS work: Drag and Drop, Copy from any other App or the Finder - then Paste into EazyDraw. Or use the Open command found on File main menu. Open for EazyDraw accepts all graphic formats understood by EazyDraw, which is most graphic formats both bitmap and vector.
For PDF, after import, if editing is desired: use Ungroup PDF from the Format -> Images menu.
Graphics from the web -- drag and drop right from the browser.
Or - from the EazyDraw main File menu, choose "New from Pasteboard".
When bitmap images are imported - a common practice is to click Uniform scale, then resize to match the size needed for your design layout.
If you are looking for artwork from the web, remember that SVG is vector and the best for subsequent editing.