It's quite hard to find inexpensive tablets that also come with good touchscreen accuracy and most tablets will try and make you pay the price for nice components. That being said I've tried to keep these options under a 700$ cap and focused on fulfilling your request of decent memory where 8gb should be more than enough for pdf editing.
The cheap option: Dell Latitude ($390)
This option comes with a Intel Core M5 6Y57 which is relatively weak as a processor but should be more than enough for word processing. The tablet also comes with a 256 GB SSD which should allow you to load documents extremely quickly and should also help with boot times. As requested this tablet comes with 8 GB Memory which should be more than enough for PDF processing. I don't have much experience with these types of tablets so the touchscreen may have something left to desire although the $800 MSRP seems to suggest that you should have a decent touchscreen.
This option sells for $390 (MSRP $800) at Newegg with free shipping.
The premium option: Microsoft Surface Pro ($538)
The Microsoft Surface line is one of Microsoft's flagship products purposely designed to combat the style and premium feel of apple laptops and as such usually comes with a higher price tag. I've personally experienced these devices as one of my close friend speaks highly of the device and uses it for notes in his University lectures. One of my professors also used this device to draw out diagrams during his lectures on the screen and did so extremely well, I might add.
While it does have a i5-4300U processor (the U tag denotes that it is a power saving processor and as such has slower performance than it's HQ, K, X, etc. counterparts) it is still has more than enough speed for lightweight pdf editing. It also comes with a 256 GB SSD and 8GB memory. The added plus is that the stylus is integrated into the pad for easy storage and the pen itself has a very fine, premium feel to it. I should also mention that the screen has 2k resolution (twice that of 1080p) which will make editing pdfs much more enjoyable to your eyes.
At a price tag of $538 (MSRP $800) at newegg with free shipping this is a solid choice if you can afford it.