To confirm, you have two different Company Files. So there's an ABC.QBW and another DEF.QBW file and you're not trying to manage both companies in a single .QBW file? Correct?
Then yes, you can give access to just that other Company File. But there are multiple way, so we'll need a little more info from you. I've given you the two most likely options down below. (And having said that, I'll probably think of others as soon as I post this...)
1) Does the remote person have QBs installed on either a work computer or on their remote computer? Or would they need to work from your computer if it is the only one with QBs installed?
2) Do you have more than one license for QBs (poss. bought a 3 User license) so that if they don't already have QBs, it's not an issue to install it on a machine for them.
3) How are they working "remotely" at the moment? Do they Remote Desktop into their computer at work? Do they have access to a company File Server? Are they truly working on their own cut off from the office and all files are just on their remote computer?
(I'm trying to get a feel for how they would access the QB file while they are Remote?)
So now some options by just taking shots in the dark. And these are also potential ways to set things up if this person is really running on their own with all files on their Remote Computer - which you really don't want....
NOTE: Depending which scenario you use, you need to understand you CANNOT WORK ON THE REMOTE FILE AND THE ONE IN THE OFFICE AT THE SAME TIME!! EVER !! You need to be very clear on who has control of the file and who is opening it at any give time. If work is done on it remotely, it MUST be sent to the office for you to work on. If you make changes in the evening, that MUST be relayed to the other person and they MUST download the latest file. Both of you working in the files at the same time can really mess things up!
You can always open the file to look at something or run a report. But you CANNOT make any changes to the file if the other person is working in their copy of the file. Less of an issue if the file stays in the office in the below scenarios.
Option 1: If the Remote Worker (RW) has QBs on their computer at work. There are a number of paid and free Remote Desktop applications that will allow the RW to access their work computer and it is basically like sitting in the office. They can user their installed QBs to access the file. You can put the file either on that computer, a File Server (if you have one) or a separate Shared Folder on your computer. (So they'd only see the .QBW file you want them to see.
You can Google Best Remote Desktop Software and do a little research on the Free and Paid versions. (I happen to use AnyDesk, but there are lots out there to choose from - Including the free one built into Windows.)
Option 2: The RW has QBs on their remote computer and they have access to the company File Sever. You can put the QB file on the File Server. But I would recommend they copy the file to their local computer, do all the work, and then upload the file back to the File Server. If you have IT people that can set up local drive on the RW computer and can confirm the integrity of the network, then that will work. But I'm assuming that's not the case, so best bet is to download, do the work, upload so you can open the file and see what has been done.
If you don't have a File Server. I'd recommend you use the MS One drive you probably have or get a DropBox account (or any of the others) to use to upload. Set it up so you both have access and can share the QB file.
QBs License is a big variable in this, so hopefully you have one to use for the RW. Otherwise that will probably be another expense. But be sure to add to yours, don't go by a totally separate single license. And yes, you can give remote access to your computer, but I don't know what else you have on there besides the other QB file. And both of you can't work on the same computer at the same time. (Access to the other QB file is not an issue. You'd just change the Password and you'd log out of that file every time.)
Odds are you'll have more questions. But shoot us the info on your current setup and we can go from there.
