How did you "convert" the file to PDF? With an external tool? Then the output may be not as expected.
If I "export to pdf" with the built in feature, I get a visible drawing on A4 size at scale 1:10.1684 to fit on the sheet.
map.pdfIf you want a PDF at scale 1:1 you have to set the paper size accordingly, 100 by 300 cm at least or a little larger if you want to include the outer text letters. Also it is advisable to change the line width to something larger than 0.00 mm, as this may be interpreted as invisible in some pdf-viewers.
Then export to PDF from within Print Preview mode with scale 1:1.
map_mod1.dxfmap_mod1.pdf