I'm used to OS X where the system PDF viewer will let you draw and write text on top of any PDF document. You can then flatten it and save as a new PDF. It saves paper and time so you can fill in any form without printing it and scanning it back to the computer.
It also lets you insert a scanned image of your signature.
Is there software for Ubuntu that would do that?
Install the PDF Import Extension from Oracle into your Extension Manager for OpenOffice and you will be able to open and edit your PDF files inside of OpenOffice Draw. Which will create all the elements (text, lines, drawings, etc.) and you will be able to remove those that you don't wish. A screenshot is here:
If you prefer to handle your pdf pages as layers and edit'em as images, then you can right click the PDF file and choose "Open with GIMP Image Editor", the "Import from PDF" dialog will show after opening gimp and will allow you to choose which pages you wish to edit with several options as shown in the next screenshot.
After which you will also be able to edit those pages as shown in this screenshot:
Good luck!
My recommendation is Xournal and its actively developed fork, Xournal++. Here are the instructions.
Install (for Xournal):
sudo apt-get install xournal
For Xournal++ you can use either the stable PPA,
sudo add-apt-repository ppa:apandada1/xournalpp-stable
sudo apt update
sudo apt install xournalpp
or the flatpak,
flatpak install flathub com.github.xournalpp.xournalpp
Run xournal or xournal++, click File>Annotate PDF, choose your PDF file.
Now, go to where you need to add your signature and click Tools>Image (or the "Image" toolbar icon), then click where you want to add the image. An image selection dialog appears, select your image.
Xournal's insert image is a great addition but not polished. As soon as you add the image make sure to resize it and move it to where you want. For resize there's no ability to ensure the proportions stay the same. Just eye it. Once you are done, it is in its own layer, which you cannot change. If you don't like how it ends up delete that layer and start again.
One handy thing is that you can use ctrl-c as soon as you resize it and then ctrl-v the next time you need to insert your image. Assuming you want the same size image this will save you some time.
When you are done choose File->Export to PDF to get it back into the PDF format I assume you'll want for sending your signed doc.
Note: A downside to Xournal is the finished document looks like the fonts are converted to an image. Fonts are no longer as crisp. Still it looks better than if you printed and rescanned and is much faster. [Note: in my most recent experience it seems this problem has been solved. Maybe I just got lucky with the particular fonts used. Please leave a comment abt your experience and I'll update accordingly.] This issue seems to be fixed in Xournal++ version 1.0.20.
Best Answer
xournal. I use it in conjunction withpython-whiteboarddaily. After you're done, just export as pdf. (The video shows how I use it.)https://www.youtube.com/watch?v=BY6ZEWNigjo