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I've been sent a pdf which contains text, vector shapes and rasterised images. I would like to take a small area of that pdf, which contains all of these, run that area though Photoshop so I can use a custom photoshop filter on it, and then take the resulting image and put it back in the original pdf.

I can open the pdf in Photoshop. That requires the whole thing to be rasterised. I can specify RBG or CMYK at that stage, and I open it in RGB-8 Adobe-1998 in Photoshop. I crop the image down to just the area I want to change. I then need to save that image out in a format that Acrobat (which I'm using to put the pdf back together) can recognise. Acrobat doesn't seem to like .psd images. However I save the image out of Photoshop, I struggle to get the same color values when I eventually insert it back into my pdf. Color values shift by more than I'd expect, despite everything having embedded profiles.

Is there a workflow that will allow me to rasterise part of a composite pdf, run it through Photoshop, and then embed that rasterised image back in the original pdf, without getting uncontrollable color shifts? I don't mind the odd 1 or 2 shift in 8-bit color value, but I'm getting much more than that. I don't have any control over the color representation of the original pdf but I can set the Photoshop up any way I want. I'm also not restricted to Acrobat. But I do need a controlled and predictable workflow.

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Don't fully understand why you'd do something like this. But if it were me... I'd open the PDF with Illustrator (things don't get rasterized). Then copy the portions needed for the "Photoshop filter" and place the .psd back in Illustrator and save as PDF. –  Scott Sep 17 '13 at 18:31
    
Thanks! I'll try that tomorrow and post the results here. –  emrys57 Sep 17 '13 at 20:00
    
I never did get to try Illustrator, sorry. But I did find a solution below that seems to work with Acrobat. –  emrys57 Sep 20 '13 at 8:44
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1 Answer

After much experiment, I have a workflow that works, although I don't know if that's just because of happenstance.

Exporting anything from the pdf did not produce predictable colors.

Instead, I opened the pdf in Photoshop. That produces a popup to select one page of the pdf to rasterise, and asks for a DPI setting and RGB/CMYK choice. I found that either RGB or CMYK would work, but that CMYK, in my case, gave smaller colour errors.

In Photoshop, I cropped the image down to the area I wanted to modify. I selected the odd shape I was interested in and made everything else in the image transparent. That's so that when I put this rectangular image back in my original pdf, I won't see a faint rectangular outline even if the color is changed one or two units.

When I had finished in Photoshop, I saved the resulting CMYK raster image out as a Photoshop pdf. I then opened that pdf in an Acrobat window, selected it and copied it, and pasted it into another Acrobat window showing my original pdf. I moved and resized the pasted rectangle to cover exactly the part of the pdf I needed to change. That gave me at most a change of one unit in color value.

I also tried saving the Photoshop image as a tiff, which allows Acrobat to insert it as an image, rather than having to open a second pdf window. That does work, but I saw changes of two units in color value.

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