Whats the best way/software that could help convert an original pdf with layers to a dwg that will be able to convert hashed lines as one continious line?
If the pdf is vectorized line work any vector based software such as Corel Draw or Adobe Illustrator could open the pdf and save as either dxf or dwg.
If the pdf is rasterized it's a whole different story as far as required software.
I use Coreldraw and Any PDF to DWG Converter (http://anydwg.com/pdf-to-dwg.html) to export PDF to AutoCAD. If the PDF file was created by AutoCAD it saves all the layers/lines/texts and entities in PDF. If the PDF file is saved as a raster file, its would not save lines and text. Any PDF to DWG Converter supports batch conversion.