How can you test the paper to make sure it is acid free when card-making and scrapbooking?

There are pens called PH testing pens that will check the acid levels of paper products. You can generally find them at craft or scrapbook stores.

Here is one online:

http://www.webyfl.com/index.asp?PageAction=VIEWPROD&ProdID=45

They are generally under $5 and a good tool to have in your scrapbook tool kit.

To remove the acid from a paper item, you can spray it with an acid removing spray. A good one is Archival Mist, although there are other ones out there.

As long as you are not directly placing photos next to or on top of papers containing acid, your projects will be fine. The acid will eventually eat through the protective papers (Such as a photo mat) but it will take YEARS.