pstoedit+ghostscript
1.download the last version pstoedit and ghostscript
2.install pstoedit and ghostscript
3 run command pstoedit -f dxf in.pdf out.dxf(make sure pstoedit can find the path of gswin32c.exe)

pstoedit+gsview
1.download the last version pstoedit and gsview
2.install pstoedit and gsview
3. use pstoedit as a plugin of gsview

pstoedit is a tool converting PostScript and PDF files into various other formats suported by different drawing editors. As a prerequesite it needs GhostScript to be installed (binary installation is sufficient).

Currently pstoedit can generate the following major formats:

• Tgif .obj format (for tgif version >= 3)
• .fig format for xfig
• pdf – Adobe’s Portable Document Format
• gnuplot format
• Flattened PostScript (with or without Bezier curves)
• DXF – CAD exchange format
• LWO – LightWave 3D
• RIB – RenderMan
• RPL – Real3D
• Java 1 or Java 2 applet
• Idraw format (in fact a special form of EPS that idraw can read)
• Tcl/Tk
• HPGL
• AI (Adobe Illustrator) (based on ps2ai.ps – not a real
  pstoedit driver – see notes below and manual)
• Windows Meta Files (WMF) (Windows  only)
• Enhanced Windows Meta Files (EMF) (Windows, but also Linux/Unix if
  libemf is available)
• OS/2 meta files (OS/2 only)
• PIC format for troff/groff
• MetaPost format for usage with TeX/LaTeX
• LaTeX2e picture
• Kontour
• GNU Metafile (plotutils / libplot)
• Skencil ( http://www.skencil.org)
• Mathematica
• via ImageMagick to any format supported by ImageMagick
• SWF
• CNC G code
• VTK files for ParaView and similar visualization tools

From above cheat, we know pstoedit supports generate DXF, but it needs the help of Ghostscript or GsView

Ghostscript is the name of a set of software that provides:
* An interpreter for the PostScript (TM) language and the Adobe Portable Document Format (PDF — sometimes confused with Acrobat, Adobe’s PDF browser/editor product), and
* A set of C procedures (the Ghostscript library) that implement the graphics and filtering (data compression / decompression / conversion) capabilities that appear as primitive operations in the PostScript language and in PDF.

reference,
GPL Ghostscript
GSview
pstoedit

Overview

pstoedit translates PostScript and PDF graphics into other vector formats.

Supported Formats

Currently pstoedit can generate the following major formats:

• Tgif .obj format (for tgif version >= 3)
• .fig format for xfig
• pdf – Adobe’s Portable Document Format
• gnuplot format
• Flattened PostScript (with or without Bezier curves)
• DXF – CAD exchange format
• LWO – LightWave 3D
• RIB – RenderMan
• RPL – Real3D
• Java 1 or Java 2 applet
• Idraw format (in fact a special form of EPS that idraw can read)
• Tcl/Tk
• HPGL
• AI (Adobe Illustrator) (based on ps2ai.ps – not a real pstoedit driver – see notes below and manual)
• Windows Meta Files (WMF) (Windows 9x/NT only)
• Enhanced Windows Meta Files (EMF) (Windows 9x/NT only)
• OS/2 meta files (OS/2 only)
• PIC format for troff/groff
• MetaPost format for usage with TeX/LaTeX
• LaTeX2e picture
• Kontour
• GNU Metafile (plotutils / libplot)
• Skencil
• Mathematica
• via ImageMagick to any format supported by ImageMagick
• SWF

Besides these some further very special formats are supported. See the
pstoedit.htm for a complete list of available
drivers.

The following formats are available as additional plugins on a
shareware basis. See http://www.pstoedit.net/plugins/
for more details.

• (Frame)Maker Intermediate Format (MIF)
• CGM Format (both binary and textual)
• SVG – scalable vector format. One candidate of the W3C
  for a web standard for vector drawings. See http://www.w3.org/Graphics/SVG/
  for more details.
• Better Enhanced Windows Meta Files (EMF) (supports curves
  and compound pathes and does more accurate text
  formatting) (Windows 9x/NT/2K/XP/Vista only)
• RTF (MS Word) (Windows 9x/NT/2K/XP/Vista only)

Use PStoEdit directly by GsView

PStoEdit has a DLL which can be used directly by GSview.
PStoEdit can be used from GSview 2.8 or later, using “Edit | Convert to vector format”.
To use PStoEdit from GSview on Windows or OS/2, unzip the PStoEdit files into c:\ghostgum\pstoedit (assuming you installed GSview to the default location c:\ghostgum\gsview).