Difference between 到处 and 处处
From Dictionary:

everywhere:
(adverb): in or to all places.
e.g. &quot;I've looked everywhere&quot;
(noun): all places or directions.
e.g. &quot;everywhere was in darkness&quot;

~

When 到处 and 处处 are used as a noun, they are interchangeable

Example:
到处都有特价 = 处处都有特价 = everywhere has discount
到处都有人 = 处处都有人 = everywhere has people
到处都有老鼠 = 处处都有老鼠 = everywhere has mice
'到处' and '处处' here are nouns with the same meaning

When it is used as an adverb, 到處 and 處處 have different meanings.


到处 = everywhere; in all place (adv)

处处 = in all aspect; in all directions; in all angles (adv)


Example:
到处查询 (ask everywhere) You go place to place and ask people there
处处查询 (ask in all aspects) You inquire all aspect of the object, e.g. Where you live? Where you work? What school you went to?
到处受阻挠 (be obstructed everywhere) e.g. Everywhere you go, you are obstructed
处处受阻挠 (be obstructed in all aspects) e.g. You want to see the boss and they say no. You try to check the bill and they refuse. You apply to transfer and it is denied
到处挑剔别人 (pick on people everywhere) e.g. you go place to place to pick on people
处处挑剔别人 (pick on people in all aspects) e.g. you complain about the coffee shop staffs work too slow. You point out someone has bad teeth. You told someone the reason of he being poor is because of his laziness
'到处' and '处处' here are adverbs with different meanings