mjhjmtu

I am working on a document using the book class, with the default font size of 10pt and default margins.

documentclass[oneside]book
usepackageblindtext

begindocument
blindtext
enddocument

I usually use Overleaf, or MiKTeX when the connection is shaky. Now, the "style" that I'm using is indeed the style that I want my final document to be in.

However, in the meantime, since I am on a 15" screen, I could really do away with those large white margins and have a better preview.

Just setting very thin margins with geometry is not what I'm looking for. I only want to crop the margins in the PDF preview, without changing the way the text looks.

The preview package with option setlengthPreviewBorder5pt is very close to what I'm aiming for, but only "in principle" since it always outputs a single page, which is not what I want.

I can try to explain it better if what I've said so far makes little sense, so do let me know.

You can use the current width/height in the geometry options:

documentclassbook
usepackage[textwidth=textwidth,textheight=textheight,
 paperwidth=dimexprtextwidth+1cm,
 paperheight=dimexprtextheight+1cm]geometry
begindocument

thetextwidth quad thetextheight

enddocument

The package geometry provides option to set text height, text width and margins. For example:

usepackage[total=6.5in,8.75in,
top=1mm, left=1mm,right=1mm, bottom=1mm]geometry

This sets textwidth=6.5in and textheight=8.75in and margins to 1mm. One can adjust the margin to required amount keeping the text area constant. The page size will be adjusted accordingly.