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I'm new here, so I apologize if this is the wrong place to ask this question.

I'm a student, and I have a 4-page PDF document of a sample test. The answers to the test questions are written on the document in blue pen; the only other colors in the document are black (the text questions) and white (the PDF background).

Is there a free, easy way to remove all instances of blue from the document? I thought something in Photoshop might work, but I unfortunately don't have access to any image editing software right now.

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    What about converting pdf to images, then using an image manipulation program to change blues to white and revombine into PDF? – davidgo Mar 31 at 4:56
  • If you can get ahold of Photoshop, yes, that will work. Photoshop will open PDF files. You could then use the color selection tool, set it to a wide tolerance, set it to include non-contiguous areas, and click on some of the blue. It will select all of the ink and then you can delete it. If it leaves some residue that was outside your tolerance range, expand the tolerance, click on some residue, and repeat. If you're using Windows (or Linux + Wine), download the free Irfanview + its plugins. That will open PDFs and my recollection is that it also has similar tools to do this. (cont'd) – fixer1234 Mar 31 at 5:22
  • Another free program is GIMP, which I believe is available for all of the major OSes. It has the tools but doesn't directly open PDFs. Use one of the free online converters to change the PDF to PNG (no artifacts, which JPG will produce). Then cleanup the PNG in GIMP. It isn't clear what you have access to or your OS, and I don't have ready access to Photoshop or Irfanview, so I'll leave this as a comment. With more detail, someone with access can flesh this out into an answer. – fixer1234 Mar 31 at 5:22
  • BTW, if you use delete, make sure the background (replacement) color is set to white. There are various ways to change blue to white. Use a selection tool that targets the ink rather than a tool that changes all blue. That will affect the color of everything else. – fixer1234 Mar 31 at 5:30

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