have you tried to put
--fullpdf --pagelayout landscape
in your code?
Please let me know if it works for you
FYI - I moved your post into the Server & Online Admin area of the forums as you're likely to get more responses here. The Community Canvas area of the site is for posting questions about how the Community site itself is working (eg why can't I upload a packaged workbook to my post?).
I've spent far too much time fighting with Tableau to get consistent viz & PDF rendering across Desktop & Server. Here are two tips besides what Zhouyi Zhang wrote:
1) Put your viz into a dashboard that has the proper sizing for your output (8 1/2 x 11, A4, etc.), then republish I always had good results with this, however if the table you're putting the dashboard into is too large then you end up getting scrollbars instead of seeing the whole table. So it's not always applicable.
2) Use the Page setup in the worksheet to set your desired layout. This would work after some fiddling because sometimes based on column width Tableau would lose columns, my memory is that also setting the worksheet to Fit Entire View was helpful.