Is it possible to directly georeference a PDF file in ArcMap?

No, it is not possible to georeference a PDF file directly in ArcMap. ArcGIS does not support PDF as an input format. The PDF file must be converted to a supported raster format, such as JPEG or TIFF, and be added to ArcMap before georeferencing.

Converting the PDF file to a supported raster format can either be done by:

• Scanning the PDF document.
• Taking a screenshot of the PDF file.
• Using an online conversion tool.
• Using the 'PDF to TIFF' tool.

Note:
In earlier versions of ArcGIS, the 'PDF to TIFF' tool is only available with the Production Mapping extension. In ArcGIS 10.3, the tool is located under Conversion Tools > From PDF.