TikZ externalize → pdf → eps → Word import = ☠

I summarize my findings. Hopefully others will find it useful.

1. Since EPS and TIFF figures were allowed, opening the EPS file in Gimp with 600dpi (with antialiasing and color/bw depending on the figure) and saving as TIFF with LZW compression made an importable figure. Despite the bitmap size of 4000x1600 and such, the file size was comparable to that of the EPS figure and looks nice.

   For some reason, trying to achieve the same with ImageMagick's convert -density=600 resulted in weird files, sometimes with monstrous sizes.

2. As @JosephWright suggested, I tried going via dvips to produce the eps. The problem is that dvips sets wrong bounding box: either it produces non-EPS file, thus having entire page as bbox, or, with -E, the bbox is too small (according to the man page, it computes the boox only from glyphs, but not from lines and other graphics which might show up in the figure).

   The solution was to use dvips -E to produce EPS file with a wrong bounding box, and then fix it with epstool (in Debian, package epstool), as suggested by @percusse. It requires a temporary EPS file (I used the .foo.eps suffix), and the setting for tikz looks like this:

   \usetikzlibrary{pgfplots.external}
   \tikzexternalize[]
   \tikzset{external/system call={latex \tikzexternalcheckshellescape -halt-on-error -interaction=batchmode -jobname "\image" "\texsource" && dvips -E -o "\image".foo.eps "\image".dvi && epstool --copy --bbox "\image".foo.eps "\image".eps && rm "\image".foo.eps "\image".dvi }}
   

   The resulting EPS is indeed importable into Word, but it is ugly (probably due to no antialiasing) and rather unusable.

Verdict:

1. EDIT - gold winner: open in IrfanView, copy, paste into Word directly (thanks to Joseph for the suggestion; I could not do that in my case)

2. silver winner: have Gimp (ghostscript) do the rendering, save as TIFF and import to Word as bitmap; word is not able to render the EPS nicely, even if it is able to load it.

3. avoid conferences where submissions must be in Word.