Purchased a 13 inch MacBook Pro with Retina Display. It came with 4GB of RAM and 128GB HD. Got it yesterday, and now I discover that you cannot upgrade the RAM to 8 or 16GB. I need to run Adobe Creative Cloud programs from time to time. Will these programs run too slow? Should I send it back?
It's pretty trivial to open Activity Monitor and look at the RAM usage.
When the graph is in RED - you will have significant slowdowns and really need to take immediate action if you require performance from all the apps running. Usually a restart will let you know if the applications you run have memory leaks and need you to quit them often, log out often, restart the OS often. Or if those apps always use a lot of RAM memory and you should either find more efficient applications to do the same work or run less apps at once or find a Machine with more RAM (assuming your Mac doesn't allow user-upgradeable RAM).
When the graph is in yellow - you're unlikely to be able to measure slow downs, but it's a signal to quit any apps you don't need (email, web browsers with dozens (or more) tabs open, social media, music streaming apps, chat apps (cough slack, cough) and let the system focus all resources to the main apps you need.
When the graph is in green - no worries about RAM being what's causing your workflow to not run at full speed. The constraints you have at that point are network, CPU, or just the apps aren't making use of the machine resources at all and need to be redesigned / updated.)
I checked out the system requirements for one of their "heavy duty" applications (Photoshop CC). The minimum is 2GB of RAM, but they recommend 8GB.
So, your application will work and should work "fairly well." But given that Adobe is recommending 8, the experience wont be great. In my experience, if they recommend 8GB, you should have 16GB
Since you just bought your rMBP, as was said earlier, now is the time to swap it out, not 3 to 6 months from now when you realize that you should have bought the one with 8GB of RAM
As an additional but of info, the 13 inch MBP is what you would call an entry level system. It does a lot and does it well but it was never meant to be a heavy lifting design machine.
The graphics card is one factor. I don't buy a Mac laptop unless it has a separate card and processor. The reason being that the Intel graphics card shares a lot of resources with the rest of the computer so if you are working on a large size file, Illustrator, for instance, will need ram and processor time to render fonts and images while OS X needs those same resources for disk access, background processes and the like.
All that has to sit somewhere and that somewhere is the ram. Think of ram like a workable. You have a small amount of ram and you have a small amount of workspace. More ram, bigger table.