How to find out any red line present in a scanned pdf , where somebody may strikes on some text or just a simple line on pdf using Python or vb.net

Question

I need to find out any red lines present in a scanned pdf file some thing like some body put a red line on pdf using Python or vb.net

we can ignore images and texts and just need to find out any red lines present in scanned pdf using python or vb.net