If you are only replacing a 6x9 foot area with no seams i would likely just replace the carpet and pad if i could find a usable pattern on roll at lowes or home depot or a remnant at a dealer.
Replace section of carpet pad.
Press it over the damaged area and turn until you reach the padding then pull out the circular piece and patch as you would a large section.
If a section of your floor covering has seen better days remember that you can patch carpet saving the considerable cost of replacing the entire thing.
Keep in mind that if you plan on replacing the carpet the patch will adhere to the padding making it harder to salvage the pad.
In either event be prepared to vacuum up a lot of dirt and possible degraded carpet pad.
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Older carpet in high traffic areas might be more faded.
A line or 2 of glue on the surface of the carpet pad will often be sufficient.