DiffPDF is developed by Mark Summerfield, I just compiled it to windows 32 version.
DiffPDF depends on poppler, poppler-qt, Qt4 library.

DiffPDF can compare two PDF files. It offers two comparison modes: Text and Appearance.
By default the comparison is of the text on each pair of pages, but comparing the appearance of pages is also supported (for example, if a diagram is changed or if a paragraph is reformatted). It is also possible to compare particular pages or page ranges. For example, if there are two versions of a PDF file, one with pages 1-12 and the other with pages 1-13 because of an extra page having been added as page 4, they can be compared by specifying two page ranges, 1-12 for the first and 1-3, 5-13 for the second. This will make DiffPDF compare pages in the pairs (1, 1), (2, 2), (3, 3), (4, 5), (5, 6), and so on, to (12, 13).

It is open source(of course free software), want to try it on your windows XP/Windows 7, please download here.

With PDF Timestamp Signer, we can create Timestamp signature on a PDF without the need of Adobe Acrobat.
You can download it from here.
This version has some limited,

• It only support create visible signature, and put the signature on the left bottom corner(100, 100, 300, 200) of the first page.
• It use http://tss.pki.gva.es:8318/tsa as timestamp server
• It only supports PKCS12 certificate file.
• It run as windows 32 console application, so it has no windows, and only run in Dos command

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