Won's print pdf files
Trouble with the HP Laserjet printed output may be solved by using the following settings (or similarly named ones):
"Use raster Graphics" (instead of "Use vector graphics"). This may fix the problem of "reversed" text (white on black background) not printing, as well as other problems.
"Download TrueType Fonts as bitmap soft fonts" (select "bitmap" instead of "outline" or "graphics"). This may remove the overlapping of text on the printed document.
"Graphics dithering" select "coarse" or "fine" (instead of "none"). This selection may improve the quality of images contained in the document. You can find all these settings in your printer properties. Go to File, Print, click Preferences, in Printing Preferences, click one by one all the top options, and change one of the top solutions, one at the time, checking your printing output.
Always check if you have the latest version of Adobe Reader Program. If not download the latest version from Adobe, it's free.
Is this the first time that you have the problem? or with the same printer (HP 4si), did you were able to print PDF files in the past?