That's DRM. It's not possible to open it with libre software.
You should complain to whoever sent that to you. In the complaint, explain
that you had to do the following (and this is what I'd suggest you do):
1. Find someone else who uses a computer with Adobe Reader on it. Ask them to
borrow their computer for a short while.
2. On this other person's computer, open the DRM-encumbered PDF in Adobe
Reader, then "print" the document to a file. Put that file onto your USB
drive (or SD card, or whatever) and transport it to your own computer.
3. Open the "printed" file from your computer and print it for real.
4. Fill out the forms by hand.
5. Use a scanner to re-convert your filled-out forms to images.
6. Paste the images into LibreOffice Draw. Export a new PDF. Send this PDF
in.
Also, be sure to include details of any difficulties you had at any one of
these steps. This will illustrate just how much of a burden they are causing
by putting handcuffs onto PDFs.
If they ask why you didn't "just" use this other person's computer to fill
out the forms, tell them that you refuse to send DRM-encumbered files out of
principle, and secondarily (if this is true) that this would hardly have made
the job easier anyway.
If they tell you that they won't accept a PDF with an image of a hand-filled
page, tell them that you will gladly fill out the PDF normally if they send a
version that can be viewed on your computer.
If they offer to help you install Adobe Reader, explain that you refuse to
put avoidable proprietary software on your computer.
