Q:

Is my new micro-sd card immune from infection on my device?

My orangepiplus2e computer has no bios, no firmware, and no hdd (other than 16GB micro-sd). It has high quality router, ethernet switch, & firewall. 
Let's say that I have files (docs,pdf,.iso) on my desktop, debian 10, that are infected. 
--- using a new micro-sd card in a new usb reader on my orangepi
--- transferring a clean OS download from the orangepi to the micro-sd on the same computer
--- I don't have any infected files open during this process
Could the new OS on the new micro-sd get infected?  
Thanks.

A:

My orangepiplus2e computer has no bios, no firmware, and no hdd (other than 16GB micro-sd).

Um, your Orange Pi Plus 2E has plenty of devices with a microcontroller and firmware that you don't control and know nothing about: The micro-SD controller, The USB controller, the Wifi chip, the Ethernet chip, and stuff on your Allwinner H3 like the Mali GPU. Think "little computers on a big computer".
As you don't know anything about these, it's possible there are hidden firmware commands that allow reflashing of those controllers. Not likely to be an issue, and not an attack vector that's used a lot in the wild, but for the sake of completeness you shouldn't forgot those.

Let's say that I have files (docs) on my desktop

BTW, the easiest way to secure documents is to make sure they are in a format that can't be executed. Like plain ASCII or UTF-8. This way you'll never have trouble with them. Executable stuff in documents is a Windows disease.

Since there is no where for the malware to go (hdd,bios,firmware), other than staying on the doc file itself,

Assuming you have some file with malware embedded and happen to execute that malware somehow, the most common path is that it installs itself into the running OS and then infects other files. Even if it was originally in a document, it needn't stay in a document; it could infect executable files. And it could do so on any kind of storage that's attached the Micro-SD, any USB sticks you connect, any network shares, ... It also can try attacks over the network.
So "there's no way for the malware to go other than staying on the document itself" is completely and utterly wrong.

And no browsers are open during this process.

This is completely irrelevant.
Judging from your question, you don't seem to have a very good mental model of what actually happens in the computer, and what the security relevant issues are. It's very dangerous to draw conclusions from such a mental model.
That said, in practice the risk of malware on Linux systems isn't that high for various reasons, so you shouldn't worry too much about it. Unless you intend to implement a high-security military application on your Orange Pi Plus 2E, or something.
Edit

For securing docs, most ".txt" or ".odt" - non-executable, yes?

Don't confuse file name suffixes with file formats. Just because a file ends in .odt doesn't mean it is actually Open Document Format. If you open such documents judging by the file name suffix, you may be in for a surprise.
Plain text is not executable. I haven't looked at Open Document in detail, but even if there are no executable extensions etc., it's complex enough that bugs may cause buffer overflows, which you could abuse to inject executable code.

As far as infected 'exe' file infecting OS, been told its just temporary unless in admin; once restart, gone.

It's true that when you restart the computer, anything in memory will be gone. However, the goal of every virus is to avoid this, so it will infect other files to make it's loaded again when the computer is rebooted.
And it can use all files accessible with current permissions to do that. So if happen to execute malware as a non-root user ("admin" on Linux is called root), there are plenty of files it could infect so it gets restarted as soon as that user logs in again.
It could also exploit bugs to raise its privilege to root; then it's game over - it could be everywhere in the file system, and you'll never going to find all places.

It would have to get to the OS first, and with my system, I don't think it could do that;

See above.

I have high quality fw, 

A firewall protects you from network attacks. It doesn't protect you from malware running on your system. As I said: You don't have a good mental model of what is actually happening on your computer (e.g., you don't understand what a Firewall does). Don't try to draw conclusions from that model in security related things.

And that's my main point and question - could it jump directly from one exe to another exe, without 1st going to the OS? 

"Going to the OS" isn't a concept that makes sense here. Think of it that way: As soon as you run malware, by using an executable or by loading a file that uses an exploit, you'll have to assume that all files that the user has permissions to access could be infected. Or, with privilege escalation exploits, even more files.

Windows, yes, everything I said makes no sense.

No. Most of what you sense makes neither sense for Windows nor Linux. (And BTW, Linux is my main OS).

Seems like hdd,bios,firmware are the bridges that allow one infected exe to infect another exe w/o OS

No.

