To me this sounds more like a bug in jspdf. Or actually in Acrobat Reader. If the program does not edit the file, who could have modified the file and how, anyway?

I don't have Acrobat Reader installed, here. Does this also happen with an empty SVG or even if you omit the call to svg2pdf altogether? There aren't that many calls that go into jspdf when the svg is empty so this might be "easy" to debug with an almost empty pdf.

According to my development team, if they create a pdf using jspdf only, Acrobat Reader does not issue the same "save changes to modified file" prompt. But if they use svgtopdf using an svg, then they get the "save changes" prompt.

My guess is that acrobat reader does not like what it's seeing in the .pdf file and is "modifying" it to its liking as it's loaded. Almost like it's "converting" it when it's opened. This is how it's becoming "modified".

Using the "playground" link above, I cleared out the text and this resulted in an empty svg. I downloaded it and still get the prompt to save the file when I close it from acrobat reader. I tried this on both chrome and edge, to be sure the browser wasn't adding anything.

Attaching 2 pdf files. Both originate from "playground" link above. I removed the "text" node and "viewbox" attribute and had it generate a pdf.
"svg2pdf_blank_before_adobe_save.pdf" is what was downloaded directly.
"svg2pdf_blank_after_adobe_save.pdf" is what the file was after adobe acrobat reader asked me to save it.
svg2pdf_blank_before_adobe_save.pdf
svg2pdf_blank_after_adobe_save.pdf

We should probably compare the output of the empty jspdf export with the "empty svg" case. The file saved by Acrobat Reader is very different from the "before" file (different file version to begin with). We'll probably need to bisect the instructions that are issued when we write the empty SVG to find out which ones Acrobat does not "like".

Using jspdf 2.5 instead of 2.0 seems to resolve the issue, can you confirm @jamesbley-rhythm?