How to export only the selected part of my Numbers file to PDF?
Unfortunately Numbers does not have a Set Print Area option in the way that MS Excel does.

It's not clear from your question how your elements are organised, but below are three options that may be useful.

Printing only a single sheet/tab

If what you want is on a single sheet, then you can:


Go to File > Print
In the Print Setup window make sure you only have This Sheet selected instead of All Sheets
Now print to PDF


Using Preview to create your PDF from a selected area

Another option is to use Preview to do this for you:


In Numbers, select the area you want on your PDF (Hint: You can use the command key to select multiple elements in different parts of the sheet)
Now copy the selected area with commandC
Open the Preview app
Go to File > New From Clipboard
Once the file appears, print it to PDF


Export to Excel first

If you happen to have access to Excel, then you could:


Export your Numbers spreadsheet to Excel
Open it in Excel
In Excel select the elements you want to print (Hint: You can use the command key to select multiple elements in different parts of the sheet)
Go to File > Print Area > Set Print Area
Now print to PDF