I need to send the file I created to an external company to print it out. However, I want to eliminate the risk of someone else using the files I created without permission.

How can I save the SVG file as an uneditable SVG file?

There is no such protection.

Your svg drawing is actually text file that defines 2D graphical objects. In order to render an image, an application must be able to read this text, which can therefore be copied and reproduced anywhere.

Svg is an open file format you can work on with a notepad only. 

Tampering with the file is always a possibility, even if that's for making a "foolproof" file for later use preventing editing some parts accidentally.

Like you can lock layers, objects, convert them to pattern fills or symbols and store in the defs section

-all of which can be reverted if that's your main goal.

Saving as pdf is oriented more towards printing and often times they are harder to be edited after.

If you want to prevent forgery I'd suggest sending an "altered" copy with some noticeable downgrading.

Like instead of an all vector content, embed a part as a jpg with a compression.

Then when investigating the issue -if there is one- you can show an initial version with higher quality the forger cannot recreate.

Sort of like an ink based stamp with its inaccurate print and ink smears.

Embedding a png with an alpha channel can turn out as a masked image in a pdf which cannot be resaved as a pdf in inkscape so maybe that's an option too.

Other than that can think of ways how to hide in parts in the svg codes by a notepad 

which by any regular alteration of the file would be missing.

However you cannot prevent people from exploring malicious intent using an svg file.

If you don't trust the printing company, don't share the file with them and look for another company or buy a printer.

One other suggestion. You can use compression software (zip file crestion,). Most of such programs have ootions to create with specific passwords. If you do this, you will want to make back up copies first. Then you can can zip one or as many files as desired, give them a unique password and when you share them, let the trusted parties know the password to un-zip and use them. The recipients would have to be trusted not to give them to others or misuse them. 

Also, you could use password protection software. Both parties would have to know how to use the software, obviously.

Or, you could duplicate the svg file and in Windows alter the extension. Such as change 001.svg to 001.xyz. the extension would have to be a unique one that other current programs do not utilize. The recipient could then just rename them back to an svg extension to use them.

No solution is perfect nor foolproof.  Humans have always been devious and can find ways to take, steal, misuse any one's work. Without regret nor acknowledgement nor just payment. It is the world we live in. As someone has shared. Lovks are only for "honest" people. Whether they are door locks or passwords or any thing else.

You can export to PDF, which creates a somewhat less useful file for future edits.
Or, export to a bitmap which is all but unusable.

You can export to PDF, which creates a somewhat less useful file for future edits.
Or, export to a bitmap which is all but unusable.  A high enough resolution bitmap will be OK for printing but not editable.