What’s new in this version?
Why the size has doubled?


Nothing much. You can see the changes here:

I don’t think the size has doubled. Which sizes are you comparing?


3.2.10638 x64 have 2118144 bytes


There are several files for each release. You didn’t say which ones exactly are you comparing.

Comparing 3.1.2-x64-install.exe to 11040-x64-install.exe, 11040 is 180 kB larger, which is within expected range.


If I not say it is because I mean the main: SumatraPDF.exe


I think your version may be a developer (z? version) they were often compacted with UPX which makes files smaller for storage and distribution however has several negative effects for executing, as UPX is not reliably reversible and adds a time penalty to loading I would not recommend its use.
I consider nowadays 9,776,032 bytes for the 64bit portable is exceptionally good value in terms of bangs per buck

the following are main changes since pre-release 10766 (32bit portable was 8,859,040 bytes now 8,912,800 bytes)

In addition to ongoing experimental Highlight and TabWidth support (may not be included in final release)

Print Driver Isolation from the print spooler service to reduce print failure. [MyNote=] This will NOT correct for a poor print driver
A6 and A2 support in command line print [MyNote=] so for CLI use MAX paper size is up from A3 to A2
Include TIFF and TIF as supported extensions [MyNote=] there are other image formats that SumatraPDF can handle
hopefully better layout for CJK (issue #250 two-bytes format, eg Chinese / Japanese /Korean)
other adjustments to improve code and numerous extensions to translations


it does not seem compressed with upx because it does not decompress.



I think @Reater has a point there seems to be “white space” in the exe

SumatraPDF-prerelease-10638-64-install.exe (2017-03-09 ) 5.03MB (5,275,792 bytes)
Unpacked 11.9 MB (12,547,224 bytes)
Main executable 2.05 MB (2,152,592 bytes)

SumatraPDF-prerelease-11040-64-install.exe (2018-08-18) 5.14 MB (5,391,264 bytes)
Unpacked 14.3 MB (15,086,536 bytes)
Main executable 4.42 MB (4,641,184 bytes)

also seeing unusual amount of “chatter” e.g. referenced comments such as “sumatra-search-across-pages-2070615.pdf” ok my bad that file was expected for testing in past pre-release


Maybe prelease is a debug version?


Yes Pre-release usually has some debug code that’s removed in formal release but by comparing between equivalent pre-release versions there should not be the size increase as you correctly pointed out.
e.g. the portable versions did NOT increase by the same factor they only increased by 0.6 %
32bit10766.exe = 8.44 MB (8,859,040 bytes)
32bit11040.exe = 8.49 MB (8,912,800 bytes)
potential size for 32bit portable release ~ 6.3 MB (6,600,000 bytes)