window.print of iframe with pdf inside bootstrap modal

Hey guys I try to print a bootstrap modal which contains an iframe pointing to a local pdf file. The modal itself looks fine.

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Problem is I want to print the modal with my own button (not the one in the pdf dialog, this works great).

<button onclick="window.print()">print page!<button />

If I do that, the pdf is cut off. This seems to happen only with pdf, not f.i. images.

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