Solid Hardwood, Engineered and Laminate Flooring - Hardwood Flooring Repairs

I have recently purchased an older home (at least 100 yrs old).
Under the carpet in the upstairs hallway I found wide planked hardwood flooring. The bad news is the underpad and carpeting have been glued to it. I have ripped up the carpeting, scrapped off the majority of the underpadding, and have started to sand the floor. The problem is that some of the boards are now a dark green, blackish colour from where the underpadding/glue was absorbed into the floor grain.
What can I do to get rid of the colour? Can I bleach the wood?
Also, please note I don't know what kind of wood it is but it is a softer wood. So I don't want to ruin it, and I don't want to replace any boards if possible, due to the age and the width of the old boards.
Your help is greatly appreciated. Tammy.

A heat gun and scraper is a frequent recommendation among forum posters for removing pad and adhesive from floors. Always scrape in direction of grain and avoid damaging the wood. There are solvent removers available for removing adhesive residue. If adhesive is absorbed into wood, sanding may not eliminate the staining problem. I had a customer who had a similar problem. She removed the pad and adhesive and had the floors professionally refinished. The adhesive continued to leach to the surface, and the stains essentially reappeared. She decided to install new hardwood over the old.