Combined pdf files with garbage fonts

I need help with creating a combined pdf document.  I start with word 2013, and use the styles to create a linked table of contents.  Then Save As to a pdf.  I deselect the Options to allow the links to work in the pdf format.  Then I add other pdf's created from word, excel or AutoCAD.  Finally I add outside pdf's from other sources (i.e. manuals) to complete the combined pdf.  Some, not all of my AutoCAD pdf's will have text changes, boxes or the letter L, basically gibberish.  I did recently change computers from a desktop to a laptop.  Running windows 8 and upgraded Acrobat Pro from X to XI.  This is extremely frustrating as it just recently seemed to start doing this.  I work for a manufacturing firm and have created combined pdf files to distribute to customers, vendors, etc. on a regular basis, and this just started.  I don't know how to fix it.  Please help