Inserting PDF makes file huge

[Art]

I just recently ran into a problem, which I was able to work around, but I
have no idea what happened.

I had an Excel file about 200K, and a PDF also about 200K. If I inserted
the PDF object and saved the Excel file it was about 400K (I'm approximating
these sizes). If I then double clicked the PDF, closed the Adobe app that
opened, and then saved the Excel file, the size went up to about 3M.

The work around that I used was the following. I began as before, inserting
the PDF. BUT, before double clicking it, I saved the Excel file and closed
it. Then I re-opened it. The size was now again about 400K. At this point
I could double click the PDF, rotate it, and basically do whatever I wanted.
When I saved the Excel file it didn't grow to 3M. I can't tell you if it got
any larger at all, but if it did, it was on the order of 1K or so.

I have no idea what happened, or why this worked. Does anyone know anything
about this?

By the way, when I inserted it, I did not save it as a link nor did I insert
it as an icon.

I'd appreciate it if anyone has any information on this.