I accidently deleted my hard drive. I am a moron, I know. After a few failed attempts at reclaiming the data, I realized all the pictures I lost are still on a single SD card I never formated.
How can I download these files and have them recognized by Lightroom with the already established picture adjustments? I know it won't have the folders to go to on my hard drive.
I don't even know where to begin
Before modifying anything, be sure to back up all your existing data (catalog and pictures) to an external source. This will make sure that whatever happens during this reconstruction work, you still have save at least the data you have currently.
If you have a backup of both, the catalog and your picture files as stored prior on your computer, then it's easy: restore and you're done. But I thought to read between the lines that you did not do backups. You should change that in the future, no matter what the work will be that you now need to invest.
The trouble for you is that you will need back at least the catalog database, where LrC keeps the edits. If you do not have access to the original catalog or to a backup your edits are lost. Fortuneatly you still have the pictures. You simply need to reimport from the card. Edits will be lost.
The complex, but more complete option is here:
If you have the catalog, you will need to rebuild the connection between the original file and the database. depending on how you work, this will be "simply" copying data from one source directory to a different one. I suggest you copy all files to the hard disk and then move files from the temporary folder to the LrC picture folder structure which is by default a root directory and a date subdirectory. If this was your structure, it may be quite easy to work your pictures back in place.
If you have a more complex structure, like having pictures anywhere on your disk, you will have a lot of work to do. If you renamed during the import, you will also redo this now.
All this needs to be done outside of lightroom, using OS tools. Normally it is not recomended to do file operations outside of LrC, but in your case it would be rebuilding the situation that LrC expects to find. You may have Lr running to have a reference of what you need to build, but you should restrain to do any work before Lr finds back the pictures at their usual place. You may close and reopen Lr in between multiple times but contrary to the standard recommendation, you should not launch a database backup before you are ready. Each time you start Lr, Lr will check the connections between the files and the database, so the more files you put back at the expected location, the less missing files will be shown in Lr.
Saving the pictures and the edits is a monster task, that will make you remind that backups are crucial.
You are probably lucky, if you still have your catalog. Do an immediate backup.
Let's say originally your pictures on your hard disk were on disk P:\ and the folder Photos.
So, you create on the disk P the folder Photos. You also create a temporary folder Scratch and copy all your pictures from the SD card to this folder. This will help you enormously a) by securing your pictures by not working on the one and only copy you still have and b) moving the files later from scratch to the final destination will be easy.
Lightroom as a default stores pictures in a directory structure starting from your root directory (here P:\Photos) and creating subfolders according to the date when the picture has been taken. First is the year, so pictures from 2021 go into P:\Photos\2021. Then there is a second subfolder for the day: 2021-05-06 if the picture has been taken on the sixth May in 2021. You need to move from scratch all pictures from that day to this destination. You do that for all pictures. The final folder path will be P:\Photos\2021\2021-05-06.
If you have a more "messy" structure, you need to follow that structure. I, personally, have different entry points for own work and customer work. And I have even for my most recurring customers a special directory. But my 4+ TB pictures will not fit on a SD card... 😉 . What I also have often are secondary edits, where I use a third-party program and LrC burns the edits to a TIFF file and those Tiff files get edited by my external programs. Those files would have been gone in a case like yours.
During the LrC import function, you can also rename files automatically. If you did do that, you need to rename all the pictures in that target directory as you did when importing. That would be the most time-consuming part, but I suggest using Bridge for this, as it has a batch renaming tool similar to the LrC functionality. Names need to be exactly as they were. If you don't know any more, LrC can show you the name, as the LrC database still knows where to find the data and how it was named... The picture will probably even show in preview, but the icon will have a question mark (file missing) attached. As soon as you have renamed, the Q-mark will go away, and the corresponding picture will be again available for working.
As you have a backup, it is worth first restoring the pictures (not the database!) to their original place and adding only the few assets that have been added after doing the backup. Edits are stored in the database, so even recent modifications on old pictures will still be OK.
It sounds like you still have your Lightroom Classic catalog, because you said:
How can I download these files and have them recognized by Lightroom with the already established picture adjustments?
Is that correct?? If so, you copy (using your operating system), not move, the photos to the EXACT SAME location they were in before (and if you don't remember, Lightroom Classic will tell you in the Metadata Panel).
The instructions I gave above will fix the problem.
"...you copy (using your operating system), not move, the photos to the EXACT SAME location they were in before (and if you don't remember, Lightroom Classic will tell you in the Metadata Panel)."
I cannot move them to the exact location because the folder structure is gone. I they will just be all my pictures in one folder.
Re-create the folders as they were. And please read carefully, I specifically said COPY not MOVE.
In the future:
Hope you had a backup of your photos.
Your old backup of the catalog, was that via LrC upon closure. Or was it a separate manual backup of say the entire folder the catalog was in? If the former, sure hope you have a backup of the photos. If the later, and that included folders with photos, then you lucked out.