Another clue. Note the file is as downloaded from the IRS with nothing filled
in. This is for pdfmod, which of course is not pdftk.
$ pdfmod f1040.pdf
[1 Debug 16:12:13.206] Starting PdfMod 0.9.1
[1 Debug 16:12:13.221] Initializing i18n catalog from /usr/share/locale/
[1 Debug 16:12:13.242] Loaded custom AccelMap from
/home/ross/.config/pdfmod/gtk_accel_map
[1 Debug 16:12:13.249] Cache directory set to /home/ross/.cache/pdfmod
[1 Debug 16:12:13.401] Loaded f1040.pdf
[3 Warn 16:12:13.442] 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
[3 Error 16:12:13.443] Error Loading Document - There was an error loading
/home/ross/Finance/tax2015/f1040.pdf
