原来PDF可以转为DXF文件的

PDFtoDXF or other Vector Graphics （PDF转 Autocad 的DXF及其他格式矢量图形）:pstoedit+Ghostscript

看到有人在论坛中询问如何把DXF格式转的PDF再转回DXF格式，可以让AUTO Cad继续修改，下面就把相关的程序介绍下：

pstoedit

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). 
依靠Ghostscript把PostScript(PS)和PDF转成其他格式(通过插件可以支持更多格式)：

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( http://www.skencil.org )
• Mathematica
• via ImageMagick to any format supported by ImageMagick
• SWF

Ghostscript
an interpreter for the PostScript language and for PDF(一个PostScript和PDF的解析器)
很多的虚拟PDF打印机程序都是依靠它来实现postscript到PDF的转换工作，开源的就有PDFCreator

安装好ghostscript 和pstoedit后，命令行的方式PDFtoDXF是：
pstoedit -f dxf in.pdf out.dxf

另外pstoedit可以做为GsView的插件来使用，至于怎么集成，中文可以看这个教程：
http://www.xdcad.net/techcenter/article/htmlcache/1031.html
Japanese Version：
http://mosoku.fc2web.com/jw_win/pdftodxf.html

至于pstoedit的其他用法，各位自己看帮助，虽然都是英文，但在下水平也不怎么样，就懒得翻译了。