I used windows Adobe Acrobat program to replace document color. It worked just fine. I saved it. Then I sent it to my android phone. I opened it in android Adobe Acrobat app and original background was there. Its strange. When I sent pdf file back to PC to check it there again, background was replaced as I intended.
Long story short (Im not native english speaker so I want to prevent confusion)
I removed background on windows desktop >
> I sent it to my adroid phone and original background was there again >
> I sent it back to my desktop and pdf file was modified (without background as I intended)