I understand that .pp3 files are located along side the original raw or in a cache location. Is there a way to have the raw edits embed into the raw files like it’s done when using ACR and avoid all these .pp3 files being created. I say that because it is easy enough to open the edited raw file in ACR and make more changes.
Mike
No, RT won’t modify the raw files.
Okay, thanks.
@stuntflyer Welcome to the forum. 
ACR won’t be able to read sidecars or metadata from other raw processors. It has its own tags and metadata. Like @heckflosse said, RT won’t modify the raw files; same with ACR.
ACR exports TIFs and DNGs, which RT could read. If you are going in the other direction, from RT to ACR, I suggest you export a TIF with as high a fidelity as possible; e.g., linear float (32-bit). ACR should be able to read most TIFs, as Adobe is a primary contributor to the TIFF spec.
afre, that is good to know. I would be going in the direction, from RT to Photoshop. I would assume that your export suggestion would apply to that program as well.
It appears that ACR does modify the raw files as the changes made in ACR are visible in Adobe Bridge. Am I missing something here?
I know this might sound complicated but we all have to start somewhere. 
No, neither app changes the raw file. It remains untouched. RT has a sidecar. ACR writes to a database or the metadata of a DNG. When the raw processor “opens” the raw file after you do an edit, the app actually accesses the sidecar, database or enclosed metadata, which is basically a record of what you did previously. That is the cool thing about raw editing. You can always remove your edits and start over, unlike JPGs.
In Bridge, you might be seeing the original preview of the raw, not the RT edit; i.e., the one you see on your camera’s LCD in review mode. If you are going from RT to ACR or PS or vice versa, I would recommend you use high bit depth (and maybe linear) TIFs.
PS What you need to do is export the TIFs in RT and then open them in ACR. Note that you won’t be working with raws, just data dense TIFs, so some ACR features (not many in recent versions, thankfully) would be inaccessible.
If you have trouble, search this forum or ask directly. There is also a handy manual: RawPedia. Start here:
So, is there any downside to storing the .pp3 files only in the cache, in order to avoid file clutter in the folder that contains the images?
Yes, the downside is that the cache is temporary. When RT or your OS decides to clear that cache, then your edits are gone.
Got it, thanks!
Storing the pp3 files in the same folder as the image files means you can just copy a folder with images and pp3 files to a different machine. If the pp3 files are stored only in cache it will be a bit more complicated.
Yup, something else I hadn’t thought about.
For what it’s worth, I prefer to have the edits saved in the metadata of the jpeg/tiff/png that the edits produced. Putting them in the raw means to me that only one edit chain is valid or current for that image, and in my workflow that’s not the case - small jpeg for proof, full-sized tiff for further editing, etc.
It’s what I do in my hack software now. My file menu has an “Open Source…” selection, where such an encoded image can be specified; what the software does is to read the edit chain from the output image, identify the starting image, open it instead of the and re-apply the edits. My workflow is fundamentally dependent on this capability.
Right now, I save the edit chain in the EXIF ImageDescription. Now that I know of the Adobe tags, I may consider modifying my software to use them instead, if they’ll support my editing semantics (that is, the chain of operations).
I still think that sidecars are the best solution. Personally, I dislike them not because of their utility but simply because they are there, like a fly on the wall you want to swat compulsively. Once I overcome that irrational part of my mind, I am okay with them. 
The “fly on the wall” is what prompted my initial post. I use Adobe bridge which allows for file groupings. Out of sight out of mind.
You know, you could always filter out the file type or even ask Bridge to ignore it all together. BTW, I thought that Bridge was no longer a thing… Oh I see, it is more of an optional thing now.
Available for free on Adobe cloud. I think it’s called bridge CC.
I mean, I thought it was discontinued. A quick web search shows that it is in maintenance mode for those who want to use it. For most users, LR is the go-to, at least that is what I think. Mind you, I haven’t used Adobe apps in ages…
I suppose that Lightroom is the go to for most people. I’m just not into the catalog system that they use.
Glenn, I know nothing about programing like yourself though I would prefer that the edits were stored in the raw data like in ACR. I rarely save to tiff for Photoshop edits. I usually just output to jpg for web viewing on a few sites. That said, rt is now my go to app for raw edits.
Congrats on your transition. 
Remember what we have been talking about. It isn’t be stored in the raw file but in a database. Having visible *.pp3s is awesome because you don’t have to worry about the database failing and losing everything, as many a LR customer would tell you that it is their deepest darkest fear.