What to Do If Your File Still Doesn’t Open
Some file formats use file extensions that are spelled almost the same, use most of the same letters but in a unique arrangement, or even use all of the same letters. However, none of those circumstances necessarily mean that the formats are identical or even related at all, so it also means they don’t necessarily open or convert in the same way.
For example, ACC files are used for both Graphics Accounts Data files and GEM Accessory files, but neither of those formats are the same and neither of them have anything to do with Microsoft Access. You most likely can not open an ACC file with any of the tools that work with ACCDB files.
The same is true for AAC, ACB and ACD (ACID Project or RSLogix 5000 Program) files. There are plenty of other file formats that could apply here, too.
If your file doesn’t open with the above suggestions, try opening it in as a text document with a text editor like one from our list of the Best Free Text Editors. It’s possible the very top or bottom, or anything in between, has some identifiable information that can help point you in the direction of what the format is, which can help lead you to a program that can open or convert your file.