Seeing all the ardunio files

I downloaded a folder that contains files, a Ardunio file, configuration.h, configuration_adv.h and a lot of other files. I moved all these files to an area where the ardunio software can access them. By going into the file menu, and using sketch you can see some of the files in the folder but not all of them. I use the pull down menu, but I still can’t see all the files.

Arduino treats a directory as a project. Normally, if you open the .ino file in a directory, all the other source files in that directory should get opened in tabs.

Yes. The .h, .c, .cpp, and .ino files should all open in tabs. What files don't open?

There are about 30 files in the folder, I can only see about 1/2 of them. If I try to use Cntl+alt+right or left arrow to scroll nothing happens. When I do the pull down menu I don’t see all the files.

Ok so here's my silly question.... I've never had anything other than the ino in the folder: why would I have other files?

why would I have other files?

It's generally considered good practice to divide up the major functions of a large program into separate modules. Sort of project-specific libraries. In the old days, this was necessary to do this to keep unused functions out of your final program to save space; it wasn't uncommon to have files containing a single function. (nowadays this is accomplished via -ffunction-sections and -gc-sections compile/link switches.)

30 files seems excessive for an Arduino-sized application, though. I'm not surprised that the IDE doesn't handle that correctly. You will probably need to make some of those files into libraries, or find a more powerful IDE (and more complex build procedure.)