Removing refrigerant from the system (evacuating) would be done by a reputable shop to capture the old refrigerant prior to working on the system (i.e, replacing a O-ring or compressor). The refrigerant really doesn't go bad, so the only reason it's evacuated it to prevent it from escaping into atmosphere as it's a potent greenhouse gas. You can top-off a system without evacuating it.
Vacuuming the system is different and is needed after it has been totally emptied (such as working on it), in order to remove all moisture from the system prior to a recharge, and to verify that the system is leak free by holding the vacuum for at least 30 minutes without it reducing. Moisture is very detrimental to refrigerant, so it all has to be removed prior to charging the system. If you are in the boat of having a totally empty system, you can rent a electric vacuum pump for free at most auto parts stores. I personally use a vacuum pump from Harbor Freight (that was around $15) which works on compressed air.
However I'd caution a DIY top-off from a can of R134A. AC systems should very, very seldomly need a top-off. If it is needing to be topped off at anything other than very infrequent intervals (say every 10 years), you probably have a leak somewhere that needs to be fixed. Typically the leaks are at O-rings or on the compressor itself. Also, you could have a problem somewhere in the system, such as an issue with the compressor or something else, that won't be fixed with a top off. A lot of those DIY topoff cans get mis-used to top off leaky systems or overcharge them, which is not good for the planet.
The best way to do this is get an actual AC manifold gauge set, which are <$100. You can then check both high and low-side pressures to diagnose problems, properly vacuum down the system if it has been emptied, and you can recharge it with basic $10 R134A cans instead of the standalone cans. Auto AC is actually pretty easy to work on, I've replaced several compressors and recharged systems from scratch using the cheapie HF manifold gauge set and air-powered vacuum pump. If you do recharge, be sure to use a can with green UV dye in it so you can spot any leaks easily.