[aldazo]

Originally Posted by orebmur

i installed my own range of stardict dictionaries according to Boyue's directions. They are properly recognized by the standalone dictionary app but not when used via the PDF reader.

Do you still have that problem? Because the solution is to create a new folder called "Dict" (without the quotes) on the internal root directory; and I'm not sure but you even can create that folder in the external (Sd) root directory. Then you need to put the new dictionary files (in stardict format) in the dict folder.
Maybe you have the issue I had: when you press on a word with the stylus it only highlight a letter so the dictionary doesn't bring a definition. In that case you have to expand the highlighted zone in a precise manner to include all the word letters, and by that I mean without including blank spaces; to accomplish that you need to let the pop-up window open and move the margins (big black dots) accordingly. The thing is that moving the margins is tedious because you need to jump to the next line to see a change.
After the word is correctly highlighted just press the "translation" button and then the "dictionary" button and voilà! you will see the definition in the (still open) pop-up window. (I know this is very convoluted and weird but the point is: we are able to look up the definition of a word with the native dictionary app using the native pdf reader application).

Originally Posted by orebmur

The reader software i liked most besides the native one is librera. While it is slightly slower it is still very usable and overall a very nicely done and versatile application. It's great how it is able to use various external dictionary apps like goldendict. Only downside is that goldendict displays nothing more but a blank page when looking up words from within librera...

I had the same problem. One solution is to install another app (like colordict, Aard, bluedict, etc). I have colordict installed but don't like how it renders on eink, I mean the black background color of the menus. Plus the font size has only 3 options: small, normal and large.
The other solution is installing a Goldendict that is not for android 4.0 or newer. I have installed the last version of goldendict (1.6.8) from this link:
http://goldendict.mobi/downloads/android/free/

So to not get the blank window, you should install
- GoldenDict-1.6.8-Android-3.0+-free.apk
- or GoldenDict-1.6.8-free.apk
but not the others. This apply to goldendict older versions too. The trade-off is that you will lose the "preferences" option, so you should not be able to change font size and many other things...which sucks. More information here:
http://goldendict.org/forum/viewtopic.php?f=6&t=7190

Other source says disabling googls chrome does the trick but I was not able to find it in the apps and the default browser cannot be disabled.

Originally Posted by JS_F

Are annotations/scribbles saved in the original PDF document or you need to export them in a new PDF file like Onyx?

From what I saw, using the native app, the annotations can be exported in html but not in pdf format. And you have 4 options: export to local, to evernote, to YouDao Cloud note or share it via QR code.
I think the annotations are not saved in the original pdf, but if you install Xodo (or whatever app with the stamp/flatten option) the annotations can be saved in a copy of the original file.