Glue residue in cottage can I just paint over it ?

I would remove it and then sand the floor to get a good even surface, otherwise your floor might not look smooth. Here are tips for removing the glue:

http://homeguides.sfgate.com/removing-glue-floors-after-tile-removal-30433.html

You'll need to remove the adhesive first. You can try scrapping it off but probably need something like this https://www.homedepot.com/p/Ready-Strip-1-gal-Mastic-Remover-MR01/100665910

NO. YOU WILL HAVE TROUBLE WITH THE PAINT ADHERING TO THE FLOOR AS IT WILL NEVER DRY PROPERLY. IT MAY BE BEST TO INSTALL VINYL TILES OR FLOORING.

Dysko is right the better the job at leveling the floor the better in the long run.

The paint will not adhere correctly

You could put some 1/4 or 1/2 thick luan plywood over the floor to give you a new smooth floor to paint on. It comes in 4 x 8 sheets and you can cut it to fit. I would NOT paint over the old adhesive.

I had a similar problem after a basement flood; vinyl flooring had been glued down and left a horrible glue residue after taken up. The pros just shook their head and couldn't offer a solution other than strong chemicals. Finally I just bought some ordinary play sand in the smallest quantity available. Used an old broom to spread it over the glue. Amazingly I could then simply scrape it up and discard. Took a very small amount of sand to solve a huge problem (over 600 SF of floor). No chemicals, just elbow grease.

I have this tin the ingredients brush on old glue. Wise metal scraper and rag to wipe off scraper. Removes paint too, wipe off residue each brushing.

I am doing old stairs to basement. D-Super Glue Remover.