What carpet tools to use?

First, what tool to use for clean cuts on high density foam carpet underlayment? I put on a new razor blade in the utility knife and all I managed to do is rip rather than cut the pad.
Second, I need to flip the carpet over to the underside for a clean cut but what the tool to use to cut it cleanly from the top? Is this tool also used to trip the edges along the wall? TIA
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I use a sharp shop utility shears (large scissors) for the underlay, and a utility knife and a steel straightedge to cut the rug.
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(Amazon.com product link shortened)25803742/sr=8-8/ref=sr_8__i4_xgl60/102-1056822-7799346?v=glance&s=hi&nY9858
I think this is the one to cut pad clean and could be used on carpets too. Looks dangerous.
(Amazon.com product link shortened)25803742/sr=8-2/ref=pd_bbs_unbuck_2/102-1056822-7799346?v=glance&s=hi&nY9858
This is the one for trimming around the edges.
(Amazon.com product link shortened)25803742/sr=8-3/ref=pd_bbs_unbuck_3/102-1056822-7799346?v=glance&s=hi&nY9858
This is a kit but I don't know how some of the tools are used. For this price they should throw in a cheap stretcher.
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Fred,

I had the same problem trying to cut the foam with a utility knife. It's easier if you compress the foam with a board or something, but a pair of sharp scissors is faster and easier.

I tried a few different "specialty" carpet tools, but wasn't very happy with the way they worked. The special "Edger" scraped up our floor trim and tended to bunch up in the carpet anyway.
In the end, I just eyeballed the cut and used a utility knife to cut it from the backside. Worked much better.
Anthony
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