There are two ways to define whether a PDF file is raster or vector:
Open a PDF file in Acrobat/Acrobat Reader. Make sure that the Selection tool for text and images is on. Then click any spot in the drawing. If the whole drawing is selected, it means your PDF is raster. If just some particular part is selected, you have a vector PDF.
Open a PDF file in Acrobat/Acrobat Reader. Zoom in any detail in the drawing with zoom level over 400%. If the contours of the selected object seem to be in high definition, smooth and clear, then it is a vector PDF. If the more you zoom in the drawing, the more blur, grainy and fuzzy it looks with clearly visible pixels, then you have a raster PDF. Please note: sometimes a PDF file may contain both vector and raster objects, that is why it is highly recommended to check several details in the drawing.