How to create the icon that precedes a file name

Inspiron 3647

In my PC Documents Folder:

1. Had a large number of Individual Folders containing various files which showed an icon(?) preceding each file name (Word, Adobe, Excel, etc.).  I believe that the icon(?) determined which reader would be used to automatically "open" the file.  I could double-click on the filename to open the file. Some of the Individual Folders had sub-folders and showed a folder icon(?) preceding the folder name.
2. I created an Aggregate Folder to contain the Individual Folders.
3. Moved Individual Folders into the newly created Aggregate Folder.
4. When I open each Individual Folder (which are now a sub-folder of the Aggregate Folder), a) the icon(?) preceding each file name is now missing, b) rather than double-clicking on the filename to open a file, I must right click the mouse to show a drop-down menu and select "open" to open the file, c) the sub-folders are now identified as folders as a type, but show no folder icon(?), cannot be opened and has a message "Size may not exceed 64K.",  d) .JPG files also show no folder icon(?) and I must right click the mouse to show a drop-down menu and select "open as" to open the file.
5. When I move a copy of a Word, Adobe or JPG file back to the PC Documents Folder, the file shows an icon(?) preceding the file name (Word, Adobe, Excel, etc.), and I can double-click on the filename to automatically open the file.
6. I suspect that when I created the Aggregate Folder there was a property setting that affects all the Individual sub-Folders, but I have not been able to find the property setting that allows the icon(?) to precede each file name and automatically determine which reader would be used to "open" a file.

Any suggestions would be appreciated.