Kindle - but also the other ebook readers - have a small screen: since a PDF is not a liquid format, either you'll end up with tiny characters or you'll have to move the virtual page on the physical screen.
In my opinion, a larger tablet in such cases is much better.
ebooks.stackexchange.com/users/106/mau
Instead of a Kindle, I bought an inexpensive tablet from a Chinese firm, which gave a large display, yet ran full Android KitKat.
Meritline.com and Everbuying.com are two vendors I've used which sell such and have been reliable for years with no problems with their products.
ebooks.stackexchange.com/users/65/K7AAY
Kindle is too small for reading PDFs and is really hard to convert them, considering the images, it doesn't worth the time.
You can try Ectaco JetBook or Sony E-reader 13.3" (too expensives).
Even a cheap tablet with anti-reflective may be a good option.
ebooks.stackexchange.com/users/3034/Apprentice
I own an original keyboard Kindle and a Samsung Tab 2 7 running Kindle
and I much prefer the tablet.
Even though it is an older model with mediocre resolution, I find that I prefer the backlight for reading at night.
And since PDF is a poor format for scaling and for transformation to Kindle format, I prefer to be able to read PDF files natively on the tablet.
So I would recommend a tablet for you.
Now, there are a number of good readers that handle formats that PDF does convert to reasonably well, or so I have read.
I have seen the Nook and the Kobo both being highly recommended for their ability to deal with almost any format.
The Kobo ARC might be a good choice as it is I believe an Android device
and you could deal with PDF natively again.
ebooks.stackexchange.com/users/3062/Kim
I have a 7" Kindle and "comfortable" is not the best way to describe the experience.
Always on landscape mode
Some books will have large fonts, giving you a "claustrophobic" sensation.
Maybe I'm overreacting but sometimes it does Books with small letters: You'll find yourself zooming in sometimes.
There are some readers that improve the experience, but, all in all, if you have the money.
Get a large screen tablet.
I'd say a 4:3 screen will give you a better reading space.
Also, there are softwares to convert them.
The end result is not good.
The Kindle version (From Amazon) also doesn't look 'right' for programming books.
Sometimes you get confused with text vs. code block.
Images and tables will break.
I have a lot of programming books and despite all that I rather read them as PDF.
It's not the perfect solution, but, it's all I have.
EDIT
: I use a mod for my Kindle, I tested a lot of readers.
ebooks.stackexchange.com/users/69/Tico
Should I buy kindle for reading PDFs only? I usually read lots of books on programming, software development and investment only. So, Should I buy kindle for the same. Because as far as I know these most of these books (Especially Programming) are available in PDF only.  Will it be comfortable reading them on Kindle?
Kindle for PDF only
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ebooks.stackexchange.com/questions/3630
ebooks.stackexchange.com/users/3021/Aman Gupta
Kindle is too small for reading PDFs and is hard to convert them. The general consensus is that a Kindle is not recommended for solely reading PDFs as they do not render well.
The general consensus is that a Kindle is not recommended for solely reading PDFs as they do not render well.