I can't open my US Tax Return in pdfmod but I can in evince. Unfortunately, as it's got too much private data, I can't post the actual PDF here.

I'm using pdfmod 0.9.1-1.in Ubuntu Natty 11.04.

From Evince's properties:
Producer: GPL Ghostscript 8.60
Creator: PScript5.dll Version 5.2.2
Format: PDF-1.4
Optimized: Yes
Security: No

And from the command line:
[1 Debug 16:47:47.585] Loaded /home/jeremy/Documents/2010-Tax-Return.pdf
[4 Warn  16:47:47.588] Caught an exception - PdfSharp.Pdf.IO.PdfReaderException: Cannot handle iref streams. The current implementation of PDFsharp cannot handle this PDF feature introduced with Acrobat 6. (in `PdfSharp')
  at PdfSharp.Pdf.IO.Parser.ReadXRefTableAndTrailer (PdfSharp.Pdf.PdfReferenceTable xrefTable) [0x00000] in <filename unknown>:0 
  at PdfSharp.Pdf.IO.Parser.ReadTrailer () [0x00000] in <filename unknown>:0 
  at PdfSharp.Pdf.IO.PdfReader.Open (System.IO.Stream stream, System.String password, PdfDocumentOpenMode openmode, PdfSharp.Pdf.IO.PdfPasswordProvider passwordProvider) [0x00000] in <filename unknown>:0 
  at PdfSharp.Pdf.IO.PdfReader.Open (System.String path, System.String password, PdfDocumentOpenMode openmode, PdfSharp.Pdf.IO.PdfPasswordProvider provider) [0x00000] in <filename unknown>:0 
  at PdfSharp.Pdf.IO.PdfReader.Open (System.String path, PdfDocumentOpenMode openmode, PdfSharp.Pdf.IO.PdfPasswordProvider provider) [0x00000] in <filename unknown>:0 
  at PdfMod.Pdf.Document.Load (System.String uri, PdfSharp.Pdf.IO.PdfPasswordProvider passwordProvider, Boolean isAlreadyTmp) [0x00000] in <filename unknown>:0 
  at PdfMod.Gui.Client+<LoadPath>c__AnonStorey10.<>m__1C () [0x00000] in <filename unknown>:0 
[4 Error 16:47:47.588] Error Loading Docu