How can one write "Please Recycle" in the context of an office paper room? I have tried: 请回收利用 but my friend says this is only for recycling batteries
I think 請回收利用/请回收利用 can apply to lots of stuff as well, for example, plastic bottles, tins, cans, glass and so on.
If you really want to be specific about recycling paper, you can try
請回收廢紙/请回收废纸 = Please recycle used/unwanted paper
請回收紙張/请回收纸张 = Please recycle paper
Note that the above Chinese examples are written in Traditional/Simplified.