Need help with a frame stl

I have been asked by my daughter in-law to make a picture frame based on a stl about 8x10

I can import the stl and create an out line vector around the outer but can’s figure out to pt one around the inner to cut that part out.

https://www.dropbox.com/scl/fi/p0kwwoa46zsxbqrdkwkji/33.STL?rlkey=4bkqhyjcolpwd19gr2h5jg6yo&st=zjaz1ah9&dl=0https://www.dropbox.com/scl/fi/p0kwwoa46zsxbqrdkwkji/33.STL?rlkey=4bkqhyjcolpwd19gr2h5jg6yo&st=zjaz1ah9&dl=0

Any direction would be appreciated.

The STL seems straight-forward enough:

(except that it needs to be repaired)

Once it is repaired, the dimensions seem a bit small:

Taking a guess as to proportion/stock size we try:

and draw a rectangle:

and import the STL into that:

and adjust the settings of the import:

Done

Switching back to the Design tab:

If we mouse over the central area we get a Z-axis height of 0.058 inches — making a note of that we switch back to the Model tab and right-click:

and choose “Create Outline Vectors”

and enter a value just slightly above the height noted

OK

which nets us the interior outline which is wanted if I understood aright.

Will, Thanks for the explanation. I had never noticed the cursor position on the bottom left corner of my screen.

I followed your examples and was able to isolate the interior portion but can’t figure out how to cut the center out completely so I can add a picture from behind. I also cannot see how to do an outer perimeter cut out of the frame.

Is there a way to set two outline vectors? I could then remove unwanted vectors from the inner and contour cut out around that vector and cut the frame outline with the other?

I have tried and don’t know how to set a second outline vector.
https://www.dropbox.com/scl/fi/7s9qkfp8az16oe4i20gty/Picure-frame-draft.c2d?rlkey=gekxgbxtrucq255vvmxqur4fb&st=k99svwgd&dl=0

I also increased the base height to thicken the frame.

Like most applications, it’s select, then affect — upload a screen grab showing the selection you are making?

Perhaps the techniques in:

and/or

and consider leaving a roughing clearance and taking a finishing pass.

Will, based upon your answer, I am not sure I worded my question properly.